Added documentation for extending optimizer and schedulers

[scap3yvt]

Fixes #N.A.

Proposed Changes

• general-purpose documentation that provides clarity

Checklist

• I have read the CONTRIBUTING guide.
• My PR is based from the current GaNDLF master .
• Non-breaking change (does not break existing functionality): provide as many details as possible for any breaking change.
• Function/class source code documentation added/updated.
• Code has been blacked for style consistency.
• If applicable, version information has been updated in GANDLF/version.py.
• If adding a git submodule, add to list of exceptions for black styling in pyproject.toml file.
• Usage documentation has been updated, if appropriate.
• Tests added or modified to cover the changes; if coverage is reduced, please give explanation.
• If customized dependency installation is required (i.e., a separate pip install step is needed for PR to be functional), please ensure it is reflected in all the files that control the CI, namely: python-test.yml, and all docker files [1,2,3].

[github-actions]

MLCommons CLA bot All contributors have signed the MLCommons CLA ✍️ ✅

[sarthakpati]

LGTM

[sarthakpati]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b3dc6fa) 94.68% compared to head (7ee7409) 94.67%.
Report is 1 commits behind head on master.

❗ Current head 7ee7409 differs from pull request most recent head d9571cb. Consider uploading reports for the commit d9571cb to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #764      +/-   ##
==========================================
- Coverage   94.68%   94.67%   -0.02%     
==========================================
  Files         117      117              
  Lines        8242     8242              
==========================================
- Hits         7804     7803       -1     
- Misses        438      439       +1     

Flag	Coverage Δ
unittests	94.67% <ø> (-0.02%)	⬇️

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