Drop SQLite support

[TheAxelander]

Due to recurrent issues with SQLite (#238 #233 #221 #219 #57) I'm thinking about dropping overall SQLite support and maybe also concentrating on stabilizing one database provider due to efforts in regression tests and updating container dependencies.

• Cleanup coding
• Rewrite Unit Test
• Check Github Actions
• Update documentation
• Check Unraid template

[mattyvau]

SQLite is still referenced in a few places in the documentation. Not sure if the remaining ones are intended, so just pointing them out.
I found:
https://theaxelander.github.io/latest/config/#database << in the line about automated database initialisation
https://theaxelander.github.io/latest/install/#build-and-deploy << where appsettings.json is referenced

[TheAxelander]

Thanks for the hint, I fixed it