[ACL-180] Add preselected scheme selection to preselected provider

[tl-luca-baggi]

Description

Add scheme_selection property to preselected provider selection.

NB the object is slightly different from the one referenced in user_selected provider selection, as it has an extra type preselected. As such, I had to refactor a bit the code and it resulted in a breaking change

I didn't find a convenient way to avoid duplicating code for common scheme selection types like InstantOnly and InstantPreferred, because of the constraints introduced by the way we serialize / deserialize objects with multiple subtypes

Type of change

Please select multiple options if required.

• 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:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where necessary
• I have added tests that prove my fix is effective or that my feature works
• I have updated the relevant documentation

[tl-luca-baggi]

Moved some classes around (e.g. created packages userselected and preselected inside schemeselection package)

[dili91]

👍