Add attribute for storing one weather warning as a whole

[marecabo]

Description:

This adds an attribute to the warning sensors from the DWD Weather warnings component. This new attribute contains the warning as a whole JSON object and thus enables the use of list-card to show the list of warnings in the UI easily.

Pull request with documentation for home-assistant.io: home-assistant/home-assistant.io#11271

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist

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:

• The manifest file has all fields filled out correctly. Update and include derived files by running python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.
  (There has not been a test for the file in the first place.)

[homeassistant]

Hi @marecabo,

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!

[springstan]

@marecabo you can rerun the checks by closing and then reopening this PR :)

The error that is preventing the FullCheck Pylint from passing is unrelevant to your particular PR and has occurred for a lot of PRs, therefore a fix has been merged to solve it.

[springstan]

Looks like a very straightforward approach to this problem! 👍

[stale]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days.
Thank you for your contributions.

[frenck]

Thanks, stalebot, but this PR awaits an initial review from us.
Please keep open for now.