[Task]: Cover Nginx Docker configuration with tests

[KevinMind]

Description

We have a (moderately) complex nginx configuration that relies on routing paths to different services, as well as serving static content from shared docker volumes.

This was broken on master for a while without anyone noticing so we should aim to cover basic functionality with some tests in CI.

Acceptance Criteria

  ### Milestones/checkpoints
  - [ ] Determine how to inject files for static content serving
  - [ ] Determine how to get a decent healtcheck per service configured in nginx
  - [ ] Implement the above in a test script that can run in CI verifying that nginx properly routes traffic

Checks

• [X] If the issue is ready to work on, I have removed the "needs:info" label.
• [X] If I have identified that the work is specific to a repository, I have removed "repository:addons-server" or "repository:addons-frontend"

┆Issue is synchronized with this Jira Task

[willdurand]

how is this different than https://github.com/mozilla/addons/issues/14886?