Add CRD versioning developer doc

[sjberman]

Problem: We need a developer doc that explains how our CRDs are versioned and what constitutes a version change.

Solution: Add a doc describing the criteria for this process.

Closes #936

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

NONE

[salonichf5]

lgtm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.84%. Comparing base (114275c) to head (e9accc3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2404   +/-   ##
=======================================
  Coverage   88.84%   88.84%           
=======================================
  Files         100      100           
  Lines        7527     7527           
  Branches       50       50           
=======================================
  Hits         6687     6687           
  Misses        784      784           
  Partials       56       56           

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[ADubhlaoich]

A few suggestions, otherwise LGTM.

Very clear.