Implement missing methods in changesetResolver and add ChangesetStats

[mrnugget]

Note to reviewers: sorry about the diff! I split up some files (example: resolvers/changesets.go into resolvers/changeset.go and resolvers/changeset_connection.go), removed old test data and old commented out tests. That makes it a bit hard to review, but I think this structure is much easier to manage in the future.

This PR fixes #12642, #12648 and #12646 by:

• Reviving the old commented out resolvers.TestCampaigns test, but not in a single test, but more manageable in the form of multiple tests: TestCampaignResolver, TestChangesetResolver, TestChangesetConnectionResolver.
• Implementing the ChangesetConnectionStats, including repository permissions (see permissions_test.go).
• Remove all the TODOs and broken stuff in the changesetResolver that was introduced when we said that a changeset can now exist in an unpublished state.

Now we have a much more solid and extensible layer of resolver tests, IMHO, that we can expand in the future. My goal here was not to go for 100% test coverage, but to test 70-80% and leave a structure that allows filling in more test cases (for merged changesets, for Bitbucket Server/Gitlab changesets, etc.)

In order to make the tests less noisy I copied over the helpers I used in service_test.go — is there a way we can de-duplicate those without running into import cycles? cc @LawnGnome

[codecov]

Codecov Report

Merging #12753 into main will increase coverage by 0.09%.
The diff coverage is 68.16%.

@@            Coverage Diff             @@
##             main   #12753      +/-   ##
==========================================
+ Coverage   50.82%   50.91%   +0.09%     
==========================================
  Files        1439     1440       +1     
  Lines       81094    81229     +135     
  Branches     6606     6552      -54     
==========================================
+ Hits        41212    41361     +149     
+ Misses      36328    36299      -29     
- Partials     3554     3569      +15     

Flag	Coverage Δ
#go	52.33% <68.16%> (+0.13%)	⬆️
#integration	24.20% <ø> (ø)
#storybook	12.72% <ø> (ø)
#typescript	47.01% <ø> (ø)
#unit	47.62% <68.16%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/frontend/graphqlbackend/campaigns.go	0.00% <ø> (ø)
enterprise/internal/campaigns/state.go	80.05% <ø> (ø)
internal/campaigns/types.go	27.70% <0.00%> (-0.03%)	⬇️
enterprise/internal/campaigns/resolvers/testing.go	59.18% <59.72%> (+0.51%)	⬆️
...terprise/internal/campaigns/resolvers/changeset.go	50.18% <62.85%> (ø)
...ternal/campaigns/resolvers/changeset_connection.go	76.31% <76.31%> (ø)
...terprise/internal/campaigns/resolvers/campaigns.go	73.87% <0.00%> (-4.51%)	⬇️
...rise/internal/campaigns/resolvers/campaign_spec.go	74.54% <0.00%> (-3.64%)	⬇️
...nterprise/internal/campaigns/resolvers/resolver.go	68.13% <0.00%> (-1.27%)	⬇️
... and 3 more

[codecov]

Codecov Report

Merging #12753 into main will increase coverage by 0.09%.
The diff coverage is 68.16%.

@@            Coverage Diff             @@
##             main   #12753      +/-   ##
==========================================
+ Coverage   50.82%   50.91%   +0.09%     
==========================================
  Files        1439     1440       +1     
  Lines       81094    81229     +135     
  Branches     6606     6552      -54     
==========================================
+ Hits        41212    41361     +149     
+ Misses      36328    36299      -29     
- Partials     3554     3569      +15     

Flag	Coverage Δ
#go	52.33% <68.16%> (+0.13%)	⬆️
#integration	24.20% <ø> (ø)
#storybook	12.72% <ø> (ø)
#typescript	47.01% <ø> (ø)
#unit	47.62% <68.16%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/frontend/graphqlbackend/campaigns.go	0.00% <ø> (ø)
enterprise/internal/campaigns/state.go	80.05% <ø> (ø)
internal/campaigns/types.go	27.70% <0.00%> (-0.03%)	⬇️
enterprise/internal/campaigns/resolvers/testing.go	59.18% <59.72%> (+0.51%)	⬆️
...terprise/internal/campaigns/resolvers/changeset.go	50.18% <62.85%> (ø)
...ternal/campaigns/resolvers/changeset_connection.go	76.31% <76.31%> (ø)
...terprise/internal/campaigns/resolvers/campaigns.go	73.87% <0.00%> (-4.51%)	⬇️
...rise/internal/campaigns/resolvers/campaign_spec.go	74.54% <0.00%> (-3.64%)	⬇️
...nterprise/internal/campaigns/resolvers/resolver.go	68.13% <0.00%> (-1.27%)	⬇️
... and 3 more

[codecov]

Codecov Report

Merging #12753 into main will increase coverage by 0.09%.
The diff coverage is 68.16%.

@@            Coverage Diff             @@
##             main   #12753      +/-   ##
==========================================
+ Coverage   50.82%   50.91%   +0.09%     
==========================================
  Files        1439     1440       +1     
  Lines       81094    81229     +135     
  Branches     6606     6552      -54     
==========================================
+ Hits        41212    41361     +149     
+ Misses      36328    36299      -29     
- Partials     3554     3569      +15     

Flag	Coverage Δ
#go	52.33% <68.16%> (+0.13%)	⬆️
#integration	24.20% <ø> (ø)
#storybook	12.72% <ø> (ø)
#typescript	47.01% <ø> (ø)
#unit	47.62% <68.16%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/frontend/graphqlbackend/campaigns.go	0.00% <ø> (ø)
enterprise/internal/campaigns/state.go	80.05% <ø> (ø)
internal/campaigns/types.go	27.70% <0.00%> (-0.03%)	⬇️
enterprise/internal/campaigns/resolvers/testing.go	59.18% <59.72%> (+0.51%)	⬆️
...terprise/internal/campaigns/resolvers/changeset.go	50.18% <62.85%> (ø)
...ternal/campaigns/resolvers/changeset_connection.go	76.31% <76.31%> (ø)
...terprise/internal/campaigns/resolvers/campaigns.go	73.87% <0.00%> (-4.51%)	⬇️
...rise/internal/campaigns/resolvers/campaign_spec.go	74.54% <0.00%> (-3.64%)	⬇️
...nterprise/internal/campaigns/resolvers/resolver.go	68.13% <0.00%> (-1.27%)	⬇️
... and 3 more

[eseliger]

You delete code everyday(🎊), when will we have negative lines of code? 🤔

[mrnugget]

@LawnGnome Went ahead and merged this, feel free to leave post-merge feedback!