[23.2] Disable admin notifications management if notifications are disabled in config

[davelopez]

Fixes #17108

When the notification system is disabled in the configuration you now get the following message:

How to test the changes?

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[martenson]

thanks @davelopez!