Add backup config storage

[MartinHjelmare]

Breaking change

Proposed change

• Add backup config storage with websocket interface.
• This store should save the automatic backup settings and data.
  • datetime of last automatic backup done (included)
  • an integer for max copies to keep (included)
  • a cron schedule string (todo)
  • a timedelta for max copies to keep (todo)
  • included data directories that should be backed up (todo)
• The logic to handle an updated config, ie what the manager should do when the config changes, will be added separately later.

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• Dependency upgrade
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• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[home-assistant]

There is a merge conflict.

[home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (backup) you are listed as a code owner for? Thanks!

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[MartinHjelmare]

After updating the config this method should take needed actions based on the new config settings. Eg reschedule the next backup.

[emontnemery]

LGTM, thanks @MartinHjelmare 👍

[MartinHjelmare]

This isn't really config, but we need to store this if we want to give consumers the last automatic backup time, regardless of the metadata of any backup files, and also if we want to be able to guard against too frequent backups eg due to DST time changes.

It'll probably also be needed to seed the backup schedule, although that implementation isn't done yet.