Improve performances for Manage pod PVC mounts (DOCLINKS)

When Manage pods mount their PVCs, in particular the DOCLINKS attachment volume, OpenShift uses the fsGroupChangePolicy setting under securityContext to control how ownership/permissions are applied to files on the volume when it is mounted.

Currently, MAS deployments do not set this field explicitly on Manage pods, so it defaults to Always, meaning OpenShift recursively walks every file on the PVC and changes ownership/permissions to match the pod's fsGroup on every pod start/restart.

For clients with very large DOCLINKS volumes (hundreds of thousands to millions of attached documents), this recursive chown/chmod operation can take several hours, directly delaying Manage pod startup and, by extension, application availability after any restart, rollout, or node reschedule.

OpenShift provides an alternative value, OnRootMismatch, which only performs the recursive ownership/permission change if the ownership of the volume's root directory doesn't already match the expected fsGroup. In practice, once the volume has been correctly set once, subsequent mounts skip the recursive walk entirely, dramatically reducing pod startup time, with no functional downside for the vast majority of deployments.

Reference (Red Hat OpenShift documentation, "Reduce pod timeouts by using fsGroup"):
https://docs.redhat.com/en/documentation/openshift_container_platform/4.20/html/storage/understanding-persistent-storage#storage-persistent-storage-fsGroup_understanding-persistent-storage

Request:

1. Preferred: Set fsGroupChangePolicy: OnRootMismatch by default on Manage pod securityContext for PVC-backed volumes (notably DOCLINKS), either at the MAS CR/operator level or via the target namespace, so that all new and existing deployments benefit without manual intervention.
2. If a global default is not feasible, then at minimum document this as an explicit post-installation best practice in the MAS/Manage installation and sizing documentation, with guidance on when it's safe to apply (i.e., not needed for small DOCLINKS volumes, but strongly recommended above a certain file count).