doc(agent): use chart-doc-gen for README rendering

[aroberts87]

What this PR does / why we need it:

Update the agent chart README to use chart-doc-gen to modernize variable documentation.

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] Title of the PR starts with type and scope, (e.g. feat(agent,node-analyzer,sysdig-deploy):)
• [x] Chart Version bumped for the respective charts
• [ ] Variables are documented in the README.md (or README.tpl in some charts)
• [x] Check GithubAction checks (like lint) to avoid merge-check stoppers
• [ ] All test files are added in the tests folder of their respective chart and have a "_test" suffix

Check Contribution guidelines in README.md for more insight.

[github-actions[bot]]

This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days

[github-actions[bot]]

This PR has been closed due to inactivity.

[github-actions[bot]]

This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days

[github-actions[bot]]

This PR has been closed due to inactivity.