feat(agent): add label for read-only agent

[ebaron]

Welcome to Cryostat! 👋

Before contributing, make sure you have:

• Read the contributing guidelines
• Linked a relevant issue which this PR resolves
• Linked any other relevant issues, PR's, or documentation, if any
• Resolved all conflicts, if any
• Rebased your branch PR on top of the latest upstream main branch
• Attached at least one of the following labels to the PR: [chore, ci, docs, feat, fix, test]
• Signed all commits: git commit -S -m "YOUR_COMMIT_MESSAGE"

---

Fixes: #996

Description of the change:

• Adds cryostat.io/read-only label to allow users to make the injected agent read-only.

Motivation for the change:

• Gives users more control over security of their injected agents

How to manually test:

1. Deploy this PR and create default CR
2. make sample_app_injected, should inject with write access turned on
3. Edit deployment with cryostat.io/read-only: true, should inject with write access turned off

[ebaron]

/build_test

[github-actions]

/build_test completed successfully ✅.
View Actions Run.

[andrewazores]

Bananas are definitely non-boolean. Approved