Rename "admin" user roles

The current user roles named "xm-admin" and "xm-sysadmin" are confusing. I propose these changes:

xm-admin => xm-repository-all

This more clearly describes the actual functionality, and sounds more like the technical enabler that it really is.

xm-sysadmin => xm-system-admin

This makes the name more consistent by avoiding compound words and following a three-part convention (useful for mapping to IAM).