Add last_used option for pipeline and explicit default

[piitaya]

Breaking changes

Assist action will open last used pipeline by default instead of preferred to be consistent with toolbar assist.

Proposed change

Adds new last_used option to assist action.

Trigger assist from the toolbar :
It will start listening on app but not on web because web users often have a keyboard on web and it will not work on insecure contexts.
It will use the last used pipeline.

Trigger assist from the assist action :
If the pipeline_id is not set, the assist action will use the last used pipeline.
If the start_listening option is not set, this assist action will not start listening on web and app.

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 Assist (external bus) payload missing details / using implied defaults #17322, fixes Assist action with 'Preferred assistant' opens last used assistant instead #17301
• 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

[balloob]

Approved. Let's wait for @jpelgrom to sign off on these changes before merging.

[jpelgrom]

Code looks good to me, thanks.