helm: support ratelimit image pull secrets and pull policy

[zhaohuabing]

This PR adds ratelimit image pull secret and image pull policy support to the helm chart.

Helm value file example:

global:
  images:
    ratelimit:
      image: "private-registry/ratelimit:master"
      pullPolicy: Always
      pullSecrets:
      - name: secret1

part of: https://github.com/envoyproxy/gateway/issues/3049

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 67.14%. Comparing base (b4a0086) to head (7692bd4). Report is 10 commits behind head on main.

:exclamation: Current head 7692bd4 differs from pull request most recent head dd8ecd7

Please upload reports for the commit dd8ecd7 to get more accurate results.

Files	Patch %	Lines
...tructure/kubernetes/ratelimit/resource_provider.go	33.33%	1 Missing and 1 partial :warning:
api/v1alpha1/kubernetes_helpers.go	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3454      +/-   ##
==========================================
- Coverage   67.36%   67.14%   -0.22%     
==========================================
  Files         166      166              
  Lines       19355    19464     +109     
==========================================
+ Hits        13039    13070      +31     
- Misses       5376     5448      +72     
- Partials      940      946       +6     

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 67.20%. Comparing base (dd35514) to head (d4f87c9).

Files	Patch %	Lines
...tructure/kubernetes/ratelimit/resource_provider.go	33.33%	1 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3454      +/-   ##
==========================================
- Coverage   67.25%   67.20%   -0.06%     
==========================================
  Files         166      166              
  Lines       19722    19723       +1     
==========================================
- Hits        13265    13255      -10     
- Misses       5503     5510       +7     
- Partials      954      958       +4     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.