MVP implementation of Backup sync agents

[ludeeus]

Proposed change

Ref: https://github.com/home-assistant/architecture/discussions/1134

Based on the proposal above, this PR implements the MVP of backup sync agents. As of now, this will only be invoked by the core backup integration. Changes to allow these to be triggered in a supervisor environment will come in a different PR.

---

So this adds:

• Allow integrations to define a async_get_backup_sync_agents function in the backup platform (as shown with the kitchen_sink integration)
• Add 3 new WS handlers to the backup integration
• Trigger backup sync if a backup is generated for the core backup integration by service call or WS.

---

Note that this PR does not yet add any tests, nor is related developer and user docs updated, this is on purpose as I expect the contents of this PR will change.

Type of change

• [ ] Dependency upgrade
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New integration (thank you!)
• [x] New feature (which adds functionality to an existing integration)
• [ ] 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

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation 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
• [ ] I have followed the perfect PR recommendations
• [ ] The code has been formatted using Ruff (ruff format homeassistant tests)
• [ ] 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

If the code communicates with devices, web services, or third-party tools:

• [ ] The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• [ ] New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• [ ] For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.

To help with the load of incoming pull requests:

• [ ] I have reviewed two other open pull requests in this repository.

[home-assistant[bot]]

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!

Code owner commands

Code owners of backup can trigger bot actions by commenting:

• @home-assistant close Closes the pull request.
• @home-assistant rename Awesome new title Renames the pull request.
• @home-assistant reopen Reopen the pull request.
• @home-assistant unassign backup Removes the current integration label and assignees on the pull request, add the integration domain after the command.
• @home-assistant add-label needs-more-information Add a label (needs-more-information, problem in dependency, problem in custom component) to the pull request.
• @home-assistant remove-label needs-more-information Remove a label (needs-more-information, problem in dependency, problem in custom component) on the pull request.

[home-assistant[bot]]

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

Code owner commands

Code owners of demo can trigger bot actions by commenting:

• @home-assistant close Closes the pull request.
• @home-assistant rename Awesome new title Renames the pull request.
• @home-assistant reopen Reopen the pull request.
• @home-assistant unassign demo Removes the current integration label and assignees on the pull request, add the integration domain after the command.
• @home-assistant add-label needs-more-information Add a label (needs-more-information, problem in dependency, problem in custom component) to the pull request.
• @home-assistant remove-label needs-more-information Remove a label (needs-more-information, problem in dependency, problem in custom component) on the pull request.

[home-assistant[bot]]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks :+1:

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[MartinHjelmare]

One test is failing.

[MartinHjelmare]

When adding new websocket commands we normally wait with merging the core PR until there's an approved frontend PR. If the API is already settled with the frontend that may not be needed.

[MartinHjelmare]

Mypy is failing.

[ludeeus]

Mypy seems happy now, docs here https://github.com/home-assistant/developers.home-assistant/pull/2434

[MartinHjelmare]

There's a merge conflict.

[ludeeus]

Until frontend has approved the questioned WS commands, I will not continue to keep it updated.

[piitaya]

Front end is merged to a feature branch. I will create a new branch when we will have changes in that PR.

[MartinHjelmare]

We'll rebase this PR to a feature branch too. :+1:

[MartinHjelmare]

This PR will be merged to the feature branch. We'll do the user docs PR when we open the feature branch PR targeting dev branch.