Parent #13329

This PR adds temporary support for Backup Download ready notifications.

Currently the notifications endpoint returns type=stat which is turned into a Stats deep link. This is not the correct behavior for the download notification. In this PR we intercept the note when it is returned from the API and swap type=stat with type=rewind-download-ready before it gets loaded into the database.

This code MUST be replaced once the API properly formats the Note (see issue #14074)

Notes
When viewing the notification detail view, the User name appears to be a link; however tapping on it will not take you anywhere. The type for this clickable range is marked as User; however User links are treated as if they are reader comment links and rely on siteId to be present in the node. In the case of backup download (and restore), the user node does not include siteId, so we can't forward the user anywhere (And I don't believe we should forward to the reader). Either way, it feels like the entire body response needs to be customized at the API level for both of these features. And we should identify where each link should forward too. Adding hacky workarounds is a poor solution.

Merge Instructions:

• Review FluxC PR merge and create a tag in FluxC develop
• Replace FluxC hash with tag from develop in build.gradle
• Remove the "Not Ready for Merge label"
• Merge this PR

To test:

• Launch the app
• Navigate to the activity log
• Tap on a item that supports backup and choose 'Download backup" from the menu
• Kick off a backup & wait until in ends
• Navigate back to the home screen
• Tap the Notifications tab
• Look for the "Your backup is ready for download" item
• Tap on the item to launch the notification detail view
• Tap on the site's Backups text (should be blue)
• Note that the Backup view is launched

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.