update rbac to support secret backend multiple providers script

[celenechang]

What does this PR do?

To support use of the secret backend multiple providers script in the agent when deployed with the Datadog Operator.

Motivation

Feature parity

Additional Notes

Anything else we should know when reviewing?

Describe your test plan

• Create a secret called test-secret (in the example below, it is in the system namespace)
• Modify the examples/datadogagent/datadog-agent-secret-backend.yaml file to include the following:

spec:
  credentials:
    apiKey: ENC[k8s_secret@system/test-secret/api_key]
    appKey: ENC[k8s_secret@system/test-secret/app_key]
    useSecretBackend: true
  agent:
    env:
      - name: DD_SECRET_BACKEND_COMMAND
        value: "/readsecret_multiple_providers.sh"
  clusterAgent:
    enabled: true
    config:
      env:
        - name: DD_SECRET_BACKEND_COMMAND
          value: "/readsecret_multiple_providers.sh"

• make sure that the agents and cluster agent start properly, and that the agent can connect to the cluster agent

[github-actions]

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[codecov-commenter]

Codecov Report

Merging #459 (e0a013c) into main (22cf913) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #459   +/-   ##
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  Coverage   60.60%   60.60%           
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  Files           3        3           
  Lines         132      132           
=======================================
  Hits           80       80           
  Misses         40       40           
  Partials       12       12           

Flag	Coverage Δ
unittests	60.60% <ø> (ø)

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[clamoriniere]

instead of documenting how to add an envvar.
should we add an option in the credentials section to select which secret backend script they want to use?

[celenechang]

I was thinking of saving this for v2, i.e. creating a SecretBackend section (and removing credentials.useSecretBackend). I could add on to the existing credentials section for now if you think it's worth doing?