Improve SunKingSHS plugin organisation

[dmohns]

Brief summary of the change made

Selection of improvements to the SunKing SHS plugin. Mostly based on learnings from the development of the Spark SHS plugin.

1. Allow users to customise the Auth and Api URL via Plugin settings.
2. Remove usage of config (and therewith env vars) in migrations as this can lead to inconsistencies.

Important

To achieve this, we allow a slightly unique solution that would otherwise be strongly discouraged. We are modifying and removing historical migration files which are using config. In this given situation it's harmless, as this is only controlling the default value of auth and api URL and the whole point of the PR is to give users to possibility to change these values.

3. Slight UI overhaul to use Widget

After:

Before:

Are there any other side effects of this change that we should be aware of?

Describe how you tested your changes?

Pull Request checklist

Please confirm you have completed any of the necessary steps below.

• Meaningful Pull Request title and description
• Changes tested as described above
• Added appropriate documentation for the change.
• Created GitHub issues for any relevant followup/future enhancements if appropriate.

[beesaferoot]

Looks good. Minor comment below