Add sequence action for automations & scripts

[frenck]

Proposed change

Context: It came out of a discussion with the UX & frontend team @ Nabu Casa when we where talking about this frontend PR: home-assistant/frontend#18470

This PR adds a new script action that can be used in automations and scripts: sequence.

The sequence action allows a user to group one of more actions into its own sequence. For example:

automation:
  - trigger:
      - platform: state
        entity_id: binary_sensor.motion
        to: "on"
    action:
      - alias: "Group of actions"
        sequence:
          - ...
          - ...
      - ...

This might not sound helpful at first, but it has quite a few use cases.

Organizing: Each sequence group can be named, but also enabled/disabled. From the automation editor perspective, a group of actions can be collapsed.

Blueprints: When using the actions selector, the author of a blueprint can ask a user for one or more action to take. However, the author of a blueprint will never be able to combine it with predefined actions (as lists in YAML are not mergable). This will now work:

automation:
  - trigger:
      - platform: state
        entity_id: binary_sensor.motion
        to: "on"
    action:
      - alias: "Some build in action"
        service: ...
      - sequence: !input user_provided_additiona_actions_from_blueprint

YAML Anchors: For our power users, YAML anchors and lists are hard. Again, lists are not mergeable, so this means it is also harder for YAML users to re-use lists of sequences. With the above, it provides a way to still be able to do this.

automation:
  - trigger:
      - platform: state
        entity_id: binary_sensor.motion
        to: "on"
    action:
      - alias: "Some action"
        service: ...
      - sequence: *anchored_list_of_actions

Parallel action: The source of this all, can be found in this PR. When the sequence action is added like is done in this PR, it becomes a generic available building block. Meaning that most of the "weirdness" or specific things done in making the UI for parallel action with sequence work... will just work without much special handling.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• 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 pull request: Handle sequences under parallel actions frontend#18470
• Link to documentation pull request: Add sequence action for automations & scripts home-assistant.io#32873

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.
• Untested files have been added to .coveragerc.

To help with the load of incoming pull requests:

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

[frenck]

Added docs PR

[edenhaus]

Thanks @frenck 👍