Fix hscim serialization

[fisx]

The SCIM requires json attribute keys to be case-insensitive, and hscim mostly implements this, but not quite, until now. This fixes this: stack test --fast hscim --test-arguments='--match "/Test.Schema.User/JSON serialization/allows casing variations in field names/"' fails on 7fbe431, but passes on 8e2ef77.

This is done by turning all keys in a JSON object to lowercase recursively

Failing tests on 7fbe431 for reference

  test-integration/Test/Spar/Scim/UserSpec.hs:330:5: 
  1) Spar.Scim.User, POST /Users, team has no SAML IdP, creates a user with PendingInvitation, and user can follow usual invitation process
       uncaught exception: ErrorCall
       responseJsonUnsafeWithMsg: ListResponse (WithMeta (WithId (Id * U) (User SparTag))) Error in $.resources[0].fields[0]: key "type" not found
       CallStack (from HasCallStack):
         error, called at src/Bilge/Response.hs:143:7 in bilge-0.22.0-2K7mJKDUfGc17BkrPwuOOW:Bilge.Response
         responseJsonUnsafeWithMsg, called at src/Bilge/Response.hs:132:22 in bilge-0.22.0-2K7mJKDUfGc17BkrPwuOOW:Bilge.Response
         responseJsonUnsafe, called at test-integration/Util/Scim.hs:260:12 in main:Util.Scim
         listUsers, called at test-integration/Test/Spar/Scim/UserSpec.hs:330:5 in main:Test.Spar.Scim.UserSpec

  To rerun use: --match "/Spar.Scim.User/POST /Users/team has no SAML IdP/creates a user with PendingInvitation, and user can follow usual invitation process/"

  test-integration/Test/Spar/Scim/UserSpec.hs:725:3: 
  2) Spar.Scim.User, POST /Users, team has no SAML IdP, doesn't list users that exceed their invitation period, and allows recreating them
       uncaught exception: ErrorCall
       responseJsonUnsafeWithMsg: ListResponse (WithMeta (WithId (Id * U) (User SparTag))) Error in $.resources[0].fields[0]: key "type" not found
       CallStack (from HasCallStack):
         error, called at src/Bilge/Response.hs:143:7 in bilge-0.22.0-2K7mJKDUfGc17BkrPwuOOW:Bilge.Response
         responseJsonUnsafeWithMsg, called at src/Bilge/Response.hs:132:22 in bilge-0.22.0-2K7mJKDUfGc17BkrPwuOOW:Bilge.Response
         responseJsonUnsafe, called at test-integration/Util/Scim.hs:260:12 in main:Util.Scim
         listUsers, called at test-integration/Test/Spar/Scim/UserSpec.hs:743:27 in main:Test.Spar.Scim.UserSpec
         searchUser, called at test-integration/Test/Spar/Scim/UserSpec.hs:725:3 in main:Test.Spar.Scim.UserSpec

  To rerun use: --match "/Spar.Scim.User/POST /Users/team has no SAML IdP/doesn't list users that exceed their invitation period, and allows recreating them/"

  test-integration/Test/Spar/Scim/UserSpec.hs:791:12: 
  3) Spar.Scim.User, GET /Users, 1 SAML IdP, finds a SCIM-provisioned user by userName or externalId
       uncaught exception: ErrorCall
       responseJsonUnsafeWithMsg: ListResponse (WithMeta (WithId (Id * U) (User SparTag))) Error in $.resources[0].fields[0]: key "type" not found
       CallStack (from HasCallStack):
         error, called at src/Bilge/Response.hs:143:7 in bilge-0.22.0-2K7mJKDUfGc17BkrPwuOOW:Bilge.Response
         responseJsonUnsafeWithMsg, called at src/Bilge/Response.hs:132:22 in bilge-0.22.0-2K7mJKDUfGc17BkrPwuOOW:Bilge.Response
         responseJsonUnsafe, called at test-integration/Util/Scim.hs:260:12 in main:Util.Scim
         listUsers, called at test-integration/Test/Spar/Scim/UserSpec.hs:791:12 in main:Test.Spar.Scim.UserSpec

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• If end-points have been added or changed: the endpoint / config-flag checklist (see Wire-employee only backend wiki page) has been followed.
• If a schema migration has been added, I ran make git-add-cassandra-schema to update the cassandra schema documentation.
• Section Unreleased of CHANGELOG-draft.md contains the following bits of information:
  • A line with the title and number of the PR in one or more suitable sub-sections.
  • If /a: measures to be taken by instance operators.
  • If /a: list of cassandra migrations.
  • If public end-points have been changed or added: does nginz need upgrade?
  • If internal end-points have been added or changed: which services have to be deployed in a specific order?

[jmatsushita]

Did a few changes to the PR description (added failing test log and what this PR does -- apart from the issue it solves). LGTM!