Add extra containers entry to inject side cars into deployment

[ab-andresc]

Proposed changes

This feature adds an extra variable to the deployment template to add extra containers.

Problem: Users would like to inject additional sidecars, these can do a variety of things.

Example: Install sigsci agent as a sidecar

https://www.fastly.com/documentation/guides/next-gen-waf/setup-and-configuration/kubernetes/kubernetes-agent-module/

Use case 2:

Do JWT validation with a separate container

Solution: Adds an entry to the template.

Testing: Manually added a sidecar, rendering looks correct.

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
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[nginx-bot]

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[github-actions]

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[ab-andresc]

I have hereby read the F5 CLA and agree to its terms

[sjberman]

Hi @ab-andresc, I'm curious about the use cases you mention. What benefit does the sigsci-agent or JWT validation do for the control plane? What connections are these sidecars handling?

[sjberman]

Per offline conversation, it seems the intention is to actually configure containers for the NGINX deployment, not the NGF control plane deployment. Since the control plane now provisions the NGINX data plane, the latter is no longer exposed directly in the helm chart. Instead, we include these configurable fields in the NginxProxy CRD and then the control plane uses that to set the deployment config when provisioning. An example of how we add a new field for this type of use case can be seen here: #3319.

[salonichf5]

Suggested change

	// ExtraContainers defines additional containers to be added to the NGINX Pod.
	// ExtraContainers defines additional containers to be added to the NGINX Pod.

[salonichf5]

it would be great if you could specify one example of the sidecars users can use.