feat: add ImagePullSecrets to PodSpec

[shahar-h]

What this PR does / why we need it:
Add ImagePullSecrets to PodSpec in order to support pulling EnvoyProxy and RateLimit images from private registries.
Use cases:

• Custom images
• Pulling images from a private mirror

Which issue(s) this PR fixes: N/A

[zirain]

I think we can learn from istio project, introduce K8SObjectOverlay, no need to add all the fields one by one.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d7d411c) 64.55% compared to head (2aa5929) 64.55%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2337      +/-   ##
==========================================
- Coverage   64.55%   64.55%   -0.01%     
==========================================
  Files         112      112              
  Lines       16072    16074       +2     
==========================================
  Hits        10376    10376              
- Misses       5043     5045       +2     
  Partials      653      653              

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[arkodg]

@zirain the UX for #2337 (comment) is not great.
I do agree we need some generic way to patch k8s fields we dont have native support for

Pulling Envoy and RateLimit from air gapped & private registries is a common use case imo

[zirain]

@zirain the UX for #2337 (comment) is not great. I do agree we need some generic way to patch k8s fields we dont have native support for

Pulling Envoy and RateLimit from air gapped & private registries is a common use case imo

it's hard to say which one is common or not.