Display unavailable backups locations

[piitaya]

Proposed change

Display unavailable backups locations and allow user to delete them (clean backup agents config).

This can happen for multiple reasons :

• user logout from cloud
• user disable integration
• user delete integration
• user delete network mount
• integration crashed (synology NAS if off)

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io