chore: Prepare v3.8.0-rc.2 release

[chewong]

What this PR does / why we need it:

Preparing for Gatekeeper v3.8.0-rc.2 release by running the following command:

make release-manifest NEWVERSION=v3.8.0-rc.2 && make promote-staging-manifest

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):
Fixes #

Special notes for your reviewer:

[codecov-commenter]

Codecov Report

Merging #1990 (f73af14) into release-3.8 (88189fd) will increase coverage by 0.06%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           release-3.8    #1990      +/-   ##
===============================================
+ Coverage        54.34%   54.41%   +0.06%     
===============================================
  Files              106      106              
  Lines             9428     9428              
===============================================
+ Hits              5124     5130       +6     
+ Misses            3916     3911       -5     
+ Partials           388      387       -1     

Flag	Coverage Δ
unittests	54.41% <ø> (+0.06%)	⬆️

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

Impacted Files	Coverage Δ
pkg/controller/config/config_controller.go	64.10% <0.00%> (ø)
...onstrainttemplate/constrainttemplate_controller.go	58.03% <0.00%> (+0.47%)	⬆️
pkg/watch/replay.go	81.25% <0.00%> (+2.27%)	⬆️

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[maxsmythe]

LGTM