use dependency_overrides in the example app

[ekuleshov]

This PR changes how FBP dependencies are pulled in into the example app.
Also removes publish_to: none from packages/flutter_blue_plus/pubspec.yaml

@chipweinberger on a side note. It might be that converting example app to SPM on the Apple platforms was somewhat premature on my side, because most consumers still have SPM disabled. Perhaps example app changes for SPM should be reverted.

[chipweinberger]

@ekuleshov , feel free to revert the changes. I made you a collaborator

[ekuleshov]

@ekuleshov , feel free to revert the changes. I made you a collaborator

@chipweinberger I can revert. Just want to coordinate.

[chipweinberger]

appreciate that :)

[chipweinberger]

update #1071 with your thoughts :)