docs(change) add breaking finalizer change info

[rainest]

What this PR does / why we need it:
Documentation for the breaking finalizer changes in #1522. This change requires manual cleanup if you used previous 2.x alpha releases.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Merging #1555 (e365d67) into next (5d72031) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             next    #1555      +/-   ##
==========================================
+ Coverage   50.48%   50.52%   +0.04%     
==========================================
  Files          92       92              
  Lines        6440     6440              
==========================================
+ Hits         3251     3254       +3     
+ Misses       2881     2879       -2     
+ Partials      308      307       -1     

Flag	Coverage Δ
integration-test	45.32% <ø> (+0.13%)	⬆️
unit-test	38.55% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
railgun/internal/ctrlutils/ingress-status.go	63.67% <0.00%> (+1.28%)	⬆️

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[shaneutt]

🙇