refactor(backend): Improve auth setup & OpenAPI generation (#10720)

Our current auth setup (`autogpt_libs.auth` + its usage) is quite
inconsistent and doesn't do all of its jobs properly. The 401 responses
you get when unauthenticated are not included in the OpenAPI spec,
causing these to be unaccounted for in the generated frontend API
client. Usage of the FastAPI dependencies supplied by
`autogpt_libs.auth.depends` aren't consistently used the same way,
making maintenance on these hard to oversee. API tests use many
different ways to get around the auth requirement, making this also hard
to maintain and oversee.
This pull request aims to fix all of this and give us a consistent,
clean, and self-documenting API auth implementation.

- Resolves #10715

### Changes 🏗️

- Homogenize use of `autogpt_libs.auth` security dependencies throughout
the backend
- Fix OpenAPI schema generation for 401 responses
  - Handle possible 401 responses in frontend
- Tighten validation and add warnings for weak settings in
`autogpt_libs.auth.config`
- Increase test coverage for `autogpt_libs.auth` to 100%
- Standardize auth setup for API tests
- Rename `APIKeyValidator` to `APIKeyAuthenticator` and move to its own
module in `backend.server`

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] All tests for `autogpt_libs.auth` pass
  - [x] All tests for `backend.server` pass
  - [x] @ntindle does a security audit for these changes
- [x] OpenAPI spec for authenticated routes is generated with the
appropriate `401` response

---------

Co-authored-by: Nicholas Tindle <nicholas.tindle@agpt.co>

.github/workflows/platform-backend-ci.yml

@@ -201,7 +201,7 @@ jobs:
           DIRECT_URL: ${{ steps.supabase.outputs.DB_URL }}
           SUPABASE_URL: ${{ steps.supabase.outputs.API_URL }}
           SUPABASE_SERVICE_ROLE_KEY: ${{ steps.supabase.outputs.SERVICE_ROLE_KEY }}
-          SUPABASE_JWT_SECRET: ${{ steps.supabase.outputs.JWT_SECRET }}
+          JWT_VERIFY_KEY: ${{ steps.supabase.outputs.JWT_SECRET }}
           REDIS_HOST: "localhost"
           REDIS_PORT: "6379"
           REDIS_PASSWORD: "testpassword"