feat: support additional volume and mounts

[boonware]

• Implements https://automation-management.ideas.ibm.com/ideas/INSTANA-I-935
• Allow users to define additional volumes and volumeMounts in the CRD. These can be useful for mounting files needed by specific sensors, for example, a keystore containing a TLS certificate needed to connect to a sensor target.

[konrad-ohms]

Thanks for your contribution, could you please add an example usage to https://github.com/instana/instana-agent-operator/blob/main/config/samples/instana_v1_extended_instanaagent.yaml ?
We try to keep examples in the repo for easy exploration of options on the CR.

I tried with a simple emtpydir for now:

...
    pod:
      volumeMounts:
      - mountPath: /cache
        name: cache-volume
      volumes:
      - emptyDir:
          sizeLimit: 500Mi
        name: cache-volume
...

I guess we would want to include an example how to mount a secret or a configmap.
A secret might make the most sense as we want to use it to mount trust stores and certificates.

It would also be great if you could add an end-to-end test in https://github.com/instana/instana-agent-operator/tree/main/e2e, but I couls also help out here, whatever you prefer 🙂 .

[konrad-ohms]

Thanks, look good

[konrad-ohms]

When having a final look, I noticed that this is actually the extended_instanaagent.yaml which shows all available options, but typically just defines the defaults.
Your changes are adding new volumes which would not reflect the default behavior, so probably it would be more consistent to have your values in that file as comment and use a separate file for the test input.
But I also realized that your e2e test is relying on the given yaml to mount the secret, so I am fine for leaving it in as is for now, I might move the test input into a new file eventually, but that should not block the release for now.