Make the Swagger UI work through the front-end proxy

[JosephMarinier]

Description:

In certain contexts, for example, our demo, the only (easy) way to access the back end API is through the front end's proxy, at /api/local/.... The Swagger UI was therefore available at /api/local/docs, but it didn't work since it was trying to fetch the spec from /openapi.json instead of /api/local/openapi.json. This PR tells the Swagger UI to fetch the spec from ./openapi.json (relative path), so it works through the front-end proxy too. This also applies to the API URL if you Try it out. Here is the screenshot of the Swagger UI as expected when accessed through the front-end API:

Before:

After:

Checklist:

You should check all boxes before the PR is ready. If a box does not apply, check it to acknowledge it.

• ISSUE NUMBER. You linked the issue number (Ex: Resolve #XXX).
• PRE-COMMIT. You ran pre-commit on all commits, or else, you
  ran pre-commit run --all-files at the end.
• USER CHANGES. The changes are added to CHANGELOG.md and the documentation, if they impact
  our users.
• DEV CHANGES.
  • Update the documentation if this PR changes how to develop/launch on the app.
  • Update the README files and our wiki for any big design decisions, if relevant.
  • Add unit tests, docstrings, typing and comments for complex sections.

[JosephMarinier]

By the way, I didn't even know 😅, but we are serving a ReDoc: https://clinc150-azimuth-pr.azurewebsites.net/redoc
It gives the same information as the Swagger UI, but in another way.

[gabegma]

Oh, wow!