Utilize HA Application credentials

[Bastian007]

Is your feature request related to a problem? Please describe.
The current installation process is a bit tricky for beginners (e.g. 404 page, user experience of selecting relevant tasklists)

Describe the solution you'd like
The new way how HA promote handling of Application credentials might help to ease initial installation and configuration and to store the credentials in a standardized way.
https://developers.home-assistant.io/docs/core/platform/application_credentials/

Describe alternatives you've considered
n/a

[myntath]

This would be a nice improvement. I had looked at some of this a while back but never really got my head around it. I will try again at some point if I find motivation, otherwise pull requests are always welcome.