Feat: add custom health check logic

[bhimrazy]

What does this PR do?

This PR introduces the ability to define custom health check logic in LitAPI, allowing users to tailor health checks to their specific needs.

Fixes #426.

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

PR review

Anyone in the community is free to review the PR once the tests have passed.
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89%. Comparing base (38b3559) to head (00f111d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #430   +/-   ##
===================================
  Coverage    89%    89%           
===================================
  Files        31     31           
  Lines      2030   2033    +3     
===================================
+ Hits       1808   1816    +8     
+ Misses      222    217    -5     

[justusschock]

Looking great. Few comments :)

[aniketmaurya]

Looks great @bhimrazy!