Allow scene configs to be merged

[Chris-V]

Description:

It is currently not possible to use scenes inside packages. This PR adds a PLATFORM_SCHEMA field to scene/__init__.py so that it can be analysed and merged on boot. Existing tests still pass locally.

Related issue (if applicable): fixes #6641

Example entry for configuration.yaml (if applicable):

Scenes configuration stays the same as defined in https://home-assistant.io/components/scene/

Checklist:

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

• Documentation added/updated in home-assistant.github.io

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

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New 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:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[mention-bot]

@Chris-V, thanks for your PR! By analyzing the history of the files in this pull request, we identified @sander76, @pvizeli and @fabaff to be potential reviewers.

[homeassistant]

Hi @Chris-V,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[Chris-V]

I'm not sure about the match_all values here. As opposed to no schema validations I guess it's not that bad, but it could be improved I guess.

[pvizeli]

You add the platfrom schema from default platform homeassistant into component. I don't think that will be correct for other platform too and they have no unittests. So you pass all test but I don't think that will be pass into real world. Mybe @balloob have a better view over all platform. You need also extend it from helper/config_validator and move that to platform self.

[MartinHjelmare]

I added config validation for scenes for a closed PR. I think that is the correct way. You can copy that if you like:
MartinHjelmare@416031f

[Chris-V]

Nice work and thanks a lot! I had very limited time this week to look at this :)

I can cherry-pick your commit in this branch or you can open another PR. This way credit is given where credit is due ;)

[MartinHjelmare]

@Chris-V
Thanks. I've opened a PR with my rebased commit. If you can test the PR to make sure that scenes can be used with packages, that would be great.