add region check upfront when user deploys interactively

[martinxu9]

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• Fix a bug that does not print the list of enabled regions in reflex deployments regions command.
• Fetch enabled regions when user deploys interactively. In this case, there is a prepare_deploy call to the hosting server. If we have a list of enabled regions, we check user input against it.
• Example of it running:
• Change the prompt for deployment name to

Choose a name for your deployed app (quiz-lime-moon):

• Add a prompt to let user confirm if they have all deps in requirements.txt if only reflex is found in there:

[picklelo]

nit: don't need the else case since the if case breaks