Add nilu air_quality platform (#19674)

* Add nilu air_pollutants platform

* Code Review - validation, DRYs, rm state override, new attr
- Repeated code moved to own method.
- Removed override of state property.
- New attr for showing nilu pollution recommendations.
- More validation of stations input.
- Minor fixes and typos.

* Removed unused prop

* Check for none result from client before entity add

* Moved platform to air_quality component

* Updated outdated docstrings

* Minor changes