Fixes #36782 - Update UI in preparation for SCA-only

[jeremylenz]

What are the changes introduced in this pull request?

Add UI messaging in preparation for the retirement of entitlement mode in Katello 4.12.

Considerations taken when implementing this change?

Once the branding plugin is updated, "Katello 4.12" will translate to "Satellite 6.16" downstream.

What are the testing steps for this pull request?

Check all of the following locations:

• Non-SCA Banner messages updated with specific Katello version (4.12) on
  • Subscriptions page
  • Legacy Content Host details page
  • Activation Key details page
• Organization Edit screen has a message next to the SCA checkbox
• SCA Banner message (Subscriptions service link) updated per UX guidance:
• For SCA organizations, banner will be removed
• The second sentence ("Learn more about your subscription usage..."), with the link to the Subscriptions service, will appear inside a Popover. This popover will be accessed by clicking a question mark icon (?) to the right of the "Subscriptions" title/header.
• The question mark icon / popover is not visible for organizations with no manifest imported.
• Also, adjusted some wording for Subscriptions page empty states.

[theforeman-bot]

Issues: #36782

[lfu]

This worked great! Nice job!