backups/manager: Emit supervisor update events on backup start/end

[3v1n0]

Proposed change

Send supervisor events to core when backups have been started and
finished so that it's possible to create automations based on such
events.

Type of change

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

Additional information

• This PR fixes or closes issue: fixes Feature Request: Snapshot complete event #2193
• This PR is related to issue:
• Link to documentation pull request: Not needed, no API changes
• Link to cli pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast supervisor tests)
• Tests have been added to verify that the new code works.

If API endpoints of add-on configuration are added/changed:

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

[3v1n0]

Something is wrong with CI... It doesn't get the cla-signed label and it fails on getting the base branch...

[pvizeli]

Thanks for your contribution. If you like to have something like this, feel free to implement the RFC for this.
#1946