Add opt-in ability to allow alpha or beta providers as part of the `upgrade-provider upstream check`

[zbuchheit]

Hello!

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Issue details

I am requesting to add the ability to opt-in for checking alpha or beta releases. An example use case is the Terraform-Meraki-Provider has been releasing their provider marked as alpha. Adding the ability to accept this for certain edge cases would make it easier to automate for certain providers.

Affected area/feature

[guineveresaenger]

Thank you for filing this issue @zbuchheit. We'll consider it in our next planning.