Y26-035 - Add universal health endpoint

[StephenHulme]

Contributes to sanger/General-Backlog-Items#700

Add /health endpoint - matches Limber equivalent

Changes proposed in this pull request

• Add built-in Rails health endpoint
• Reorder routes definitions to be more logically grouped

Instructions for Reviewers

• It might be easier to inspect the PR by commit.

[All PRs] - Confirm PR template filled
[Feature Branches] - Review code
[Production Merges to main]
    - Check story numbers included
    - Check for debug code
    - Check version

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.21%. Comparing base (a794def) to head (78d0499).
⚠️ Report is 10 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5550   +/-   ##
========================================
  Coverage    87.21%   87.21%           
========================================
  Files         1459     1459           
  Lines        32902    32902           
  Branches      3456     3456           
========================================
  Hits         28695    28695           
  Misses        4186     4186           
  Partials        21       21           

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