Finish servantifying brig

[fisx]

https://wearezeta.atlassian.net/browse/WPB-8691

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[akshaymankar]

Lets gooooo 🚀

[fisx]

Federator.API
  Inward
    should return 404 'no-endpoint' response from Brig [✘]

Failures:

  test/integration/Test/Federator/InwardSpec.hs:100:13: 
  1) Federator.API.Inward should return 404 'no-endpoint' response from Brig
       uncaught exception: ErrorCall
       Missing response body.

  To rerun use: --match "/Federator.API/Inward/should return 404 'no-endpoint' response from Brig/"

happens locally and on CI, but only on this branch, not on develop.