standardize groupID and userid

What does this MR do and why?

Set high-UID user (> 10000) to avoid conflicts with the host’s user table.

Same group UID is set for the sake of consistency.

Note: security context for metal3-ironic and meta3-mariadb pods are not changed for the moment. This would require to make changes to images, since these are the default IDs for respectively Ironic and MariaDB. The issue will be addressed later.

Related reference(s)

https://kubesec.io/basics/containers-securitycontext-runasuser/

Test coverage