update appconfig migration to handle existing record

[adamsachs]

Closes #2779

Code Changes

• include a server_default of encrypted {} value when creating the config_set column in migration, so as to handle cases where an existing appconfig record exists while allow the new column to be nullable.

Steps to Confirm

• see issue description for repro steps

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation:
  • documentation complete, PR opened in fidesdocs
  • documentation issue created in fidesdocs
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

Description Of Changes

the proposed solution is not ideal - i'm not sure of a truly clean way to handle this. the column in question here is a new column in 2.8.x and it's an encrypted JSON column that ideally should be non-nullable. before this change, the problem with the migration was that it just added the non-nullable column to the table, but doesn't account for the fact that there may be an existing record in the db, even though that's quite a narrow edge case. but in that case, the new non-nullable column is added to the record, but the column is obviously null since it didn't exist, and that's the error we get.

the "obvious" fix would be to give that column a server_default when creating it in the migration, so that it's not null. but i don't think we can do effectively that from the context of the migration, since it's encrypted JSON, and it's not like the migration has access to the app encryption key. UPDATE - i was totally wrong about this, thanks to @pattisdr for showing me that we do indeed have access to the app encryption key in the migration. so this is the path i've decided on now!

it's worth noting that this is handling a pretty narrow edge case - but @RobertKeyser did run into it on a migration of an internally hosted app, so it's worth us fixing!

[cypress]

Passing run #710 ↗︎

0	3	0	0	0
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Details:

Merge 4a8d593 into 0602e8b...
Project: fides	Commit: a5d59b6c96 ℹ️
Status: Passed	Duration: 00:36 💡
Started: Mar 9, 2023 6:25 PM	Ended: Mar 9, 2023 6:26 PM

_{This comment has been generated by cypress-bot as a result of this project's GitHub integration settings.}

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (f5ae75a) 86.55% compared to head (4a8d593) 86.55%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2780   +/-   ##
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  Coverage   86.55%   86.55%           
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  Files         291      291           
  Lines       16488    16488           
  Branches     2117     2117           
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  Hits        14272    14272           
  Misses       1817     1817           
  Partials      399      399           

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[pattisdr]

this looks fine! I've provided some other optional paths, but this is good too.