Add policy endpoints

[codeEmpress1]

Done

• Add the following endpoints
  • [GET] /admin/store/<store_id>/models/<model_name>/policies
  • [POST] /admin/store/<store_id>/models/<model_name>/policies

How to QA

• login with login-beta
• GET:
  • go to https://snapcraft-io-4333.demos.haus/admin/store/njwQYXFnS7ppo7LaGxoh7aqVZc1CPi26/models/alimot_test_model2/policies
  • go to https://snapcraft-io-4333.demos.haus/admin/store/njwQYXFnS7ppo7LaGxoh7aqVZc1CPi26/models/alimot_test_model/policies
• POST:
  • the post endpoint should be tested using a front end client with payload {"signing_key": string sha3-384}

Issue / Card https://warthogs.atlassian.net/browse/WD-4659

Fixes #

Screenshots

[webteam-app]

Demo starting at https://snapcraft-io-4333.demos.haus

[codecov]

Codecov Report

Merging #4333 (46e4d95) into main (cc529ab) will decrease coverage by 15.27%.
The diff coverage is n/a.

❗ Current head 46e4d95 differs from pull request most recent head 499d438. Consider uploading reports for the commit 499d438 to get more accurate results

@@             Coverage Diff             @@
##             main    #4333       +/-   ##
===========================================
- Coverage   86.83%   71.56%   -15.27%     
===========================================
  Files          95      101        +6     
  Lines        6720     3088     -3632     
  Branches        0      801      +801     
===========================================
- Hits         5835     2210     -3625     
+ Misses        885      756      -129     
- Partials        0      122      +122     

Flag	Coverage Δ
javascript	71.56% <ø> (?)
python	?

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see 196 files with indirect coverage changes

[Lukewh]

👍 LGTM