feat(agent): add pod mutation webhook to inject agent

[ebaron]

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---

Fixes: #970

Description of the change:

• Adds a mutating admission webhook for pods that responds to a pair of labels by injecting the Cryostat agent and configuring it to work with the specified Cryostat instance.

Motivation for the change:

• Makes it much easier to set up the Cryostat agent with arbitrary pods.

How to manually test:

1. make deploy
2. make create_cryostat_cr
3. make sample_app
4. Modify the sample app deployment as follows:
   1. Override JAVA_OPTS_APPEND to not inject the built-in Cryostat agent.

      - env:
        - name: JAVA_OPTS_APPEND
          value: -Dquarkus.http.host=0.0.0.0 -Djava.util.logging.manager=org.jboss.logmanager.LogManager -Dio.cryostat.agent.shaded.org.slf4j.simpleLogger.defaultLogLevel=debug
      

   2. Add the following labels:

      cryostat.io/name: cryostat-sample
      cryostat.io/namespace: cryostat-operator-system
      

   3. I had to also increase the memory limit to prevent OOM.
5. The sample application should appear as an agent target in Cryostat

I've filed issues for the TODOs in this PR. There are a few of them, but they're all pretty small compared to this PR:
#992, #993, #994, #995, #996

[andrewazores]

I added a config sample to do DEPLOY_NAMESPACE=$(oc project -q) make sample_app_agent_injected for test convenience. Seems to work nicely!

[ebaron]

/build_test

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[andrewazores]

Other than the minor comments above this seems to be working quite well. Exciting to see!

[ebaron]

/build_test

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[andrewazores]

Just needs rebasing. I'm relieved to see that there are no conflicts with #923 :-)