add API version in HTTP headers

[ghubertpalo]

Content

This patch adds a new HTTP response header that advertise the version of the Mithril Protocol supported by the server.

Pre-submit checklist

• Branch
  • [ ] Tests are provided (if possible)
  • [X] Commit sequence broadly makes sense
  • [X] Key commits have useful messages
• PR
  • [X] No clippy warnings in the CI
  • [X] Self-reviewed the diff
  • [X] Useful pull request description
  • [X] Reviewer requested
• Documentation
  • [ ] Update README file (if relevant)
  • [ ] Update documentation website (if relevant)
  • [ ] Add dev blog post (if relevant)

Comments

Issue(s)

Relates to #YYY or Closes #YYY

[github-actions[bot]]

Unit Test Results

    3 files  ±0    28 suites  ±0   2m 33s :stopwatch: -20s 326 tests ±0  326 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0  379 runs  ±0  379 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0 

Results for commit 8e45da1d. ± Comparison against base commit 9714e2c9.

:recycle: This comment has been updated with latest results.