[#197] Klanten API migration command

[SonnyBA]

Fixes #197

Changes

Adds a management command which allows the migration of the previous Klanten API to the Klantinteracties API. Two running instances (Klanten and Klantinteracties API) are required to do so with an API token for the Klanten API.

[stevenbal]

Looks good overall, I think it might also be good to add some basic documentation on how to use this command to the docs

[stevenbal]

@SonnyBA I haven't worked on this yet, since I've spent most of my time on zgw consumers upgrade for Open Zaak. Could you pick up the feedback for this PR?

[joeribekker]

Refinement: Waiting for @SonnyBA to get better. If not this week, @annashamray will pick it up.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.43066% with 36 lines in your changes missing coverage. Please review.

Project coverage is 96.72%. Comparing base (a8d5aa1) to head (423ed1a).
Report is 63 commits behind head on master.

Files with missing lines	Patch %	Lines
src/openklant/migration/v1/data.py	90.43%	11 Missing ⚠️
src/openklant/management/commands/migrate_to_v2.py	91.83%	8 Missing ⚠️
src/openklant/migration/test_server.py	38.46%	8 Missing ⚠️
src/openklant/migration/client.py	88.23%	6 Missing ⚠️
src/openklant/tests/vcr.py	85.71%	2 Missing ⚠️
src/openklant/migration/v2/data.py	96.87%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #263      +/-   ##
==========================================
- Coverage   96.89%   96.72%   -0.17%     
==========================================
  Files         146      167      +21     
  Lines        6444     7668    +1224     
==========================================
+ Hits         6244     7417    +1173     
- Misses        200      251      +51     

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[SonnyBA]

Requires #280

Edit: Since #280 was merged, this PR was rebased (see below)

[SonnyBA]

@stevenbal I moved code from the management command file to the migration folder inside the django project dir, this makes things more readable in my opinion (separate folders for v1/v2 definitions) instead of having everything in one file. I also moved the cassettes to the migration folder inside of the project root where there also is a fixtures directory (which is used for the docker compose setup).

[alextreme]

@SonnyBA please round up this PR and release a new version of Open Klant with in

[stevenbal]

Some small questions/remarks, otherwise it looks good 👍

[stevenbal]

formatting is off for this:

you might have to use .. code-block:: bash

[SonnyBA]

Good catch! That fixed it:

[stevenbal]

Only one remark about docs formatting, otherwise good to merge for me 👍