Support templates in action target

[karwosts]

Proposed change

Support templates in visual editor for action target field. We currently support it for all subfields of data, but not for target until now.

There is sometimes a bit of jankiness where messing with the selector will kick the user out of visual editor and back to yaml mode due to superstruct validation, but I didn't come up with a great solution that doesn't undesirably weaken the validation for other cases not involving templates.

E.g. in the example screenshot, if you add the key area_id: to the object selector you'll be temporarily kicked out of visual editor because the struct validator asserts that area_id cannot be null. We could add to the validator that area_id is allowed to be null, but I don't know if we want that. Or if you're editing the target template, and you remove the template identifier "{{", you'll be kicked out of visual mode because the superstruct asserts that if target is a string it must be a template.

I think that's not too bad of a tradeoff to support this though, it would be a fairly rare occurence to be making edits like that.

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 Templates in automations and scripts #25639
• 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