Ensure rebuild authorized_keys works

What does this MR do?

Adds a warning message, and provides the ability to permanently enable the "Write to authorized_keys file" setting as the first part of the rake task.

I added the enable prompt because almost anyone running this rake task:

1. Wants the setting to be enabled
2. Expects it to be enabled
3. Is unaware of the setting (and should be using the appropriate default)

Why was this MR needed?

All EE installations that were upgraded to 9.3.0 had writing to authorized_keys disabled by default. This was corrected and rebuilt for all installations as of 9.3.3, with the exception of installations where "Save" was clicked in Admin Area > Settings while running 9.3.0, 9.3.1, or 9.3.2.

A warning message was given for these installations (automatic correction was impossible without modifying installations that were intentionally disabled) during migrations in the 9.3.3 upgrade, but this has proven inadequate for notifying potentially affected customers.

Screenshots (if relevant)

Answering "yes"

Answering "no"

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #2883 (closed)