test(sampleapp): configure Cryostat Agent sample app to use k8s serviceaccount token auth

[andrewazores]

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See #928
See cryostatio/cryostat-agent#383

Description of the change:

Reconfigures the make sample_app_agent to use the automatic Kubernetes serviceaccount token detection for authentication/authorization to the auth proxy. This will automatically in OpenShift. In other Kubernetes environments the user will need to patch the resulting Deployment to add CRYOSTAT_AGENT_AUTHORIZATION or CRYOSTAT_AGENT_AUTHORIZATION_TYPE+CRYOSTAT_AGENT_AUTHORIZATION_VALUE environment variables to match any oauth2-proxy Basic authentication that may be optionally configured.

Motivation for the change:

Exercises the latest best practice of using injected serviceaccount tokens managed by cluster RBAC, rather than using hardcoded long-lived tokens as part of the Deployment spec.

This probably still isn't exactly the best practice, as this grants the Role to the whole workload application and not only its Agent, so it's adding extra privileges to the workload that are not strictly required. It is useful and convenient as an example for testing and development, to demonstrate how the serviceaccount token system works with the Agent and the auth proxy, and it's better than giving the Agent an admin user token via environment variable which was commonly done for testing before.

The even more ideal situation is to configure the Agent with TLS client certificates properly and have it talk to the new TLS gateway proxy. I think that would be a good setup to exercise as a new sample app configuration at some point.

How to manually test:

1. Get an OpenShift cluster
2. Install Operator
3. Create a Cryostat CR named cryostat-sample, ex make create_cryostat_cr
4. make sample_app_agent
5. Open Cryostat UI and ensure that the sample application appears on the Topology view. This may take a bit of time but should be relatively short.