Add if/else automation/script action

[frenck]

Proposed change

This PR adds support for an if action.
Although these constructs could already be created using the existing choose action, the choose action resembles/acts more as an switch statement.

I'm suggesting adding this construct for simplification of code and clarity. Especially with smaller conditional actions, the choose statement adds quite some overhead (and would not be the action one would think of using).

The goal is to create readable and understandable automations:

action:
  if:
    condition: state
    entity_id: light.living_room
    state: "on"
  then:
    service: light.turn_off
    entity_id: light.living_room

else case is supported too (although no practical use for this example, it does illustrate it):

action:
  if:
    condition: state
    entity_id: light.living_room
    state: "on"
  then:
    service: light.turn_off
    entity_id: light.living_room
  else:
    service: light.turn_on
    entity_id: light.living_room  

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)
• 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 frontend pull request: Add if/else automation/script action frontend#12301
• Link to documentation pull request: Add if/else automation/script action home-assistant.io#22342

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 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.

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To help with the load of incoming pull requests:

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

[frenck]

I think its ready to go!