fix: helm warning when setting NetworkPolicy ingress rule(s)

[sebastian-stephan]

What this PR does / why we need it:

When setting custom ingress rules for the NetworkPolicy via controllerManager.networkPolicy.ingress, helm spits out a warning, because the default value is set to { } instead of an array.

Example Values:

controllerManager:
  networkPolicy:
    enabled: true
    ingress:
      - from:
        - ipBlock:
          cidr: 0.0.0.0/0

Helm Warning:

coalesce.go:286: warning: cannot overwrite table with non table for gatekeeper.controllerManager.networkPolicy.ingress (map[])

This fixes it by setting the default value to an empty array.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 47.99%. Comparing base (3350319) to head (73148da).
Report is 143 commits behind head on master.

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HEAD has 1 upload less than BASE

Flag	BASE (3350319)	HEAD (73148da)
unittests	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3541      +/-   ##
==========================================
- Coverage   54.49%   47.99%   -6.50%     
==========================================
  Files         134      218      +84     
  Lines       12329    15167    +2838     
==========================================
+ Hits         6719     7280     +561     
- Misses       5116     7070    +1954     
- Partials      494      817     +323     

Flag	Coverage Δ
unittests	47.99% <ø> (-6.50%)	⬇️

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[JaydipGabani]

Thanks for the PR! lgtm

[maxsmythe]

LGTM