break up https on axis tests (for better detection of 400 Bad request failure rate) and add DKRZ NGINX tests

[valeriupredoi]

Description

Disentangle unit tests for the https case; add DKRZ server tests too. The "All tests pass" box below is a bit funny 😁

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

• This pull request has a descriptive title and labels
• This pull request has a minimal description (most was discussed in the issue, but a two-liner description is still desirable)
• Unit tests have been added (if codecov test fails)
• Any changed dependencies have been added or removed correctly (if need be)
• If you are working on the documentation, please ensure the current build passes
• All tests pass

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.13%. Comparing base (0cfce52) to head (cb5b5c9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #332   +/-   ##
=======================================
  Coverage   93.13%   93.13%           
=======================================
  Files           7        7           
  Lines         685      685           
=======================================
  Hits          638      638           
  Misses         47       47           

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