feat(admission-controller,sysdig-deploy): add initial support for cert-manager

[yurrriq]

What this PR does / why we need it:

Fixes #1761

Checklist

• Title of the PR starts with type and scope, (e.g. feat(agent,node-analyzer,sysdig-deploy):)
• Chart Version bumped for the respective charts
• Variables are documented in the README.md (or README.tpl in some charts)
• Check GithubAction checks (like lint) to avoid merge-check stoppers
• All test files are added in the tests folder of their respective chart and have a "_test" suffix

[github-actions]

Hi @yurrriq. Thanks for your PR.

After inspecting your changes someone with write access to this repo needs
to approve and run the workflow.

[yurrriq]

Given an existing ClusterIssuer/selfsigning-isser:

apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: selfsigning-issuer
spec:
  selfSigned: {}

... and the following values to a release of sysdig-deploy:

admissionController:
  enabled: true
  webhook:
    ssl:
      certManager:
        enabled: true
        issuer:
          name: selfsigning-issuer

... the sysdig-deploy and admission-controller charts do what I'd expect:

• create a Certificate for the ValidatingWebhookConfiguration, using the existing ClusterIssuer/selfsigning-issuer
• don't include any caBundle in the webhooks
• annotate the ValidatingWebhookConfiguration so cainjector will inject the cert bundle

[yurrriq]

This was the laziest way I could think of to avoid reimplementing this template.

[yurrriq]

I'm not sure what the thinking is behind all the $existingVac logic, so I just skipped it here.

[yurrriq]

Note that I don't inject any Cert value here so the resulting ValidatingWebhookConfiguration manifest won't contain any caBundle as per the _helper.tpl changes above.

[yurrriq]

There's a lot we could parameterize here, but I figure we should start simple and can always iterate.

[yurrriq]

I've deliberately done it this we so we can easily add a boolean parameter like webhook.ssl.certManager.issuer.create later to determine whether we should create an issuer.

[airadier]

CC @mavimo @AlbertoBarba which team should review and merge? I assume we want to port the changes to the cluster-shield chart too

[airadier]

@yurrriq thanks so much for this contribution! We are going to review internally and also port the changes to the cluster-shield chart, as this is now the official deployment method for Admission Controller.

Thanks again.