fix: only set matchConditions on webhook when not empty

[martijnvdp]

What this PR does / why we need it:
only set matchConditions on webhooks when the list in values is not empty

empty matchConditions gets ommited by kubernetes and when deploying with argoCD it results in a drift on this property

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 #3410

Special notes for your reviewer:

[ritazh]

@martijnvdp Thanks for the PR! Gatekeeper helm chart is autogenerated when a release is cut.
Please refer to https://open-policy-agent.github.io/gatekeeper/website/docs/help#contributing-to-helm-chart to make the change in the necessary place and run make manifests. Thank you!

[martijnvdp]

thanks i have updated the PR

[Sir-Jacques]

Any updates on this?

We are running the ignoreDifferences workaround for now, but would like to get rid of that if possible.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.74%. Comparing base (3350319) to head (843bdeb).
Report is 95 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (3350319) and HEAD (843bdeb). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (3350319)	HEAD (843bdeb)
unittests	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3412      +/-   ##
==========================================
- Coverage   54.49%   46.74%   -7.76%     
==========================================
  Files         134      218      +84     
  Lines       12329    14784    +2455     
==========================================
+ Hits         6719     6911     +192     
- Misses       5116     7069    +1953     
- Partials      494      804     +310     

Flag	Coverage Δ
unittests	46.74% <ø> (-7.76%)	⬇️

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[ritazh]

LGTM

[sozercan]

LGTM

[maxsmythe]

LGTM

[JonnieDoe]

Any updates on this?

We are running the ignoreDifferences workaround for now, but would like to get rid of that if possible.

We are also impacted on 3.16.x