Introduce default userroles for author, editor webmaster, cmsadmin and admin groups

We now have a precise set of userroles which are assigned by default to the default provided user groups (author, editor, webmaster, cmsadmin, admin), and these are configured using the new .meta:add-new-values (HCM-283).

Thus, if a downstream project wants/needs to customize or these default userroles assignments, they can do so without these customization's being overwritten by the default product configuration.

Except: when we in the future introduce more and additional 'default' userroles assigned to these groups. Then, the first initial bootstrap will still add/apply them.

We can however further and completely decouple this possible 'interfering' with project specific usages and configuration of these groups by introducing a dedicated default userrole for each of these groups which aggregate (imply) the default to be assigned userroles.
Those default group userroles, named "xm-default-<group->user" then is what is maintained and its implied userroles possibly extended depending on the (future) standard feature a project uses. Note: the standard provided userroles are of config category.
The default 'group' userroles also become convenient for projects using external user/group providers (e.g. LDAP, OIDC, etc.).

A downstream project can decide to just use the default groups and/or these default group level userroles, or create custom "group" userroles instead (or simply maintain/assign the desired userroles for a group directly).

Summarizing, this issue will introduce and change the following:

• new default group level userroles:
  • xm-default-author-user
  • xm-default-editor-user
  • xm-default-webmaster-user
  • xm-default-cmsadmin-user
  • xm-default-sysadmin-user (for group admin)
• provide and set the single initial userrole for the corresponding groups, which thereafter never needs to be updated anymore
• likewise, the standard admin user (which no longer is member of the admin group) also just gets the xm-default-sysadmin-user userrole set
• likewise, the relevance-user (targeting project) also no longer needs to be member of the webmaster group and just gets the xm-default-webmaster-user userrole set