fixes #8477 - usability improvements to template locking/defaults

- In practice, locking templates without the ability to unlock them doesn't seem to work (see the foreman_discovery issue that would be fixed by #7480).
- Provide a warning for templates that are shipped by default by plugins
- Exposes the 'default' option to users so they can mark templates to be automatically seeded or not
- Mark foreman templates as default on new installs

If this or something like this is taken, I can remove the code from Katello seeds that touches Foreman templates.
Sorry if I'm missing something... trying to understand this change, but I don't think this plus the other recommendation captures all 4 scenarios:

- If taxonomies are fully disabled, don't show this option
- If only locations are enbaled, user must have rights to create them
- If only orgs enabled, user must have rights to create them
- If both are enabled, user must have rights to both