this PR adds support for configuring the Coder deployment'ssecurityContext (for both pod & container) in the values file. this comes in handy when deploying Coder on OpenShift, which appliesSecurityContextConstraints to deployments.

one question i have - since the Coder deployment consists of a single container, is it necessary for us to have a pod-levelsecurityContext? thesecurityContext set at the container-level takes precedence over the pod-level context.

keeping thepodSecurityContext values is beneficial if there is any possibility of us adding containers to the deployment. otherwise, I don't see much a reason to keep it.