Lovelace: Move migrate to separate WS command

[balloob]

Description:

Move Lovelace migration to a separate WS command, to be called by UI after confirming with the user.

Related issue (if applicable): fixes #

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#<home-assistant.io PR number goes here>

Example entry for configuration.yaml (if applicable):

Checklist:

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

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New or updated dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

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

[houndci-bot]

Some files could not be reviewed due to errors:

Traceback (most recent call last):

Traceback (most recent call last):
  File "/home/linters/.local/bin/flake8", line 7, in 
    from flake8.main.cli import main
ModuleNotFoundError: No module named 'flake8'

[zsarnett]

I believe this is a good compromise. Will this auto set new users up UI Editing? I think asking current users is a good idea as it would change the way they currently write their files. But new users should have to opt out as we want to push users to use the UI editor

[balloob]

This will set up new users automatically, as they have no cards, so no cards that need IDs