Clarify Settings migrated to projects generated from Templates
### Problem to solve
Related to https://gitlab.com/gitlab-org/gitlab/-/issues/461846
When creating a project from a template, it's not clear which settings are copied.
Our [documentation states](https://docs.gitlab.com/ee/user/group/custom_project_templates.html#what-is-copied-from-the-templates) the following is copied:
> * Branches
> * Commits
> * Tags
But then also in the same section says:
> To learn more about what is migrated, see [Items that are exported.](https://docs.gitlab.com/ee/user/project/settings/import_export.html#project-items-that-are-exported)
Which adds many examples:
> Project configuration
>
> Merge requests
>
> Merge request approvers
>
> Push rules
>
> etc...
In practice we can see some settings are copied over, but fail to work correctly as shown in https://gitlab.com/gitlab-org/gitlab/-/issues/461846 for merge request rules when using a group of approvers.
### Further details
### Proposal
Clarify exactly what can be copied from a template, and what cannot
issue