Add room hint support to Google Assistant cloud

[balloob]

Description:

Allow configuring room hints for Google Assistant entities.

Related issue (if applicable): fixes #

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#5274

Example entry for configuration.yaml (if applicable):

cloud:
  google_actions:
    entity_config:
      switch.test:
        room: living room

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code does not interact with devices:

• Tests have been added to verify that the new code works.