Adds support for unique id

[marvin-w]

Description

This PR adds experimental (opt-in) support for unique ids within the KNX platform. Since XKNX natively does not have the ability to provide unique ids we created our own ones based on data that we think might be unique across an installation.

This PR is tested and working correctly on my local test setup:

You can see that with the unique_id feature turned on you can set customize the entity to your liking.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• The documentation has been adjusted accordingly
• The changes generate no new warnings
• Tests have been added that prove the fix is effective or that the feature works
• The changes are documented in the changelog
• The Homeassistant plugin has been adjusted in case of new config options

[coveralls]

Coverage decreased (-0.2%) to 94.743% when pulling a656bf2 on marvin-w:feature/unique_id into 63d2630 on XKNX:main.

[farmio]

🤔 when we add value_template to Sensor and BinarySensor users could be tempted to create multiple Entities with the same state_address but different value_templates. This would result in UID duplicates.

[marvin-w]

@farmio How should we continue here?

For the value_template stuff - we could just add the value template to the unique_id for sensors

[marvin-w]

I adjusted the unique id for scenes to include the scene number.

As the value_template stuff has been declined by HA upstream I would not worry about it too much.

[kifort]

Big thank you @marvin-w! I can finally start using the home assistant areas with KNX :)