Add JSON attribute topic to MQTT sensor

[emontnemery]

Description:

Add JSON attribute topic to MQTT sensor in same way as supported by MQTT binary sensor (#18923).

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

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
• There is no commented out code in this PR.

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

• Documentation added/updated in home-assistant.io

[OttoWinter]

LGTM - docs are missing

[fabaff]

@emontnemery, can you please squash when you are merging?

[emontnemery]

Yes, sorry about that! Should I revert and merge again?

[fabaff]

No, just for the future. The release helper script is getting the data from the commit history.

"Squash and merge" is unfortunately not the default.

[Fonta]

The deprecated warning might need some clarification in the docs.
I've updated to 0.85.0b0 yesterday and now I'm getting 4 of these warnings while I'm not using "json_attributes".

[emontnemery]

@f0nt4 There shouldn't be a warning if you're not using json_attributes, can you please open a new issue for that?

[Fonta]

There we're some retained topics from testing a script to automatically create notifications for low batteries. I'm not using the script anymoer so I've cleared the topics and the warnings are now gone.

https://github.com/notoriousbdg/Home-AssistantConfig/blob/master/packages/battery_alert.yaml