Make --find-interpreter require opt-in to prereleases

[davidhewitt]

Followup to #1960 (comment)

I think that probably when using --find-interpreter maturin should ignore prereleases unless an additional --allow-prereleases flag is passed. I think this would help avoid users accidentally uploading wheels for prerelease Python versions before they are ready to deliberately be testing them in CI.

(Maybe it can print that it found them and give a hint to add --allow-prereleases, but not build for them.)

[fatelei]

i want to have a try

[messense]

@fatelei Thanks, let us know if you have any questions.