Add getProvider function

[friedger]

Is your feature request related to a problem? Please describe. When I have more than one extension installed, it is confusing which extension popups first.

Describe the solution you'd like The library should provide a function that determines which extension to use, similar to https://github.com/friedger/stacks-send-many/blob/main/src/lib/getProvider.ts

Describe alternatives you've considered Let the user experience bad UX

Additional context Especially with asigna, users will have usually at least two extension installed.

Credits go to @hozzjss