WIP: Mqtt discovery updates rework

[jbouwh]

Proposed change

Code for handling MQTT discovery updates for platforms without entities was specialized for notify. tag and device_automation. This PR moves the discovery logic and device updates to a centralized place.

For notify the discovery topic is now reset when the device is removed to avoid rediscovery after a restart.
This was already implemented for the tag platform.

DONE: notfify and tag
TODO: device_automation

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
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Checklist

• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

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  Updated and included derived files by running: python3 -m script.hassfest.
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[probot-home-assistant]

Hey there @emontnemery, mind taking a look at this pull request as it has been labeled with an integration (mqtt) you are listed as a code owner for? Thanks!
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[jbouwh]

This PR is superseded by #67966.