fix(agent): place readOnly attributes for sysfs-vol correctly

[jacalvo]

What this PR does / why we need it:

repos/charts ‹sysdig-deploy-add-fs-mount*›$ helm upgrade -n sysdig-agent sysdig-agent charts/sysdig-deploy
Error: UPGRADE FAILED: error validating "": error validating data: ValidationError(DaemonSet.spec.template.spec.volumes[8]): unknown field "readOnly" in io.k8s.api.core.v1.Volume

repos/charts ‹jacalvo/fix-sysdig-deploy-add-fs-mount›$ helm upgrade -n sysdig-agent sysdig-agent charts/sysdig-deploy
Release "sysdig-agent" has been upgraded. Happy Helming!

Checklist

• Title of the PR starts with type and scope, (e.g. feat(agent,node-analyzer,sysdig-deploy):)
• Chart Version bumped for the respective charts
• Variables are documented in the README.md (or README.tpl in some charts)
• 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