build_release_candidate.sh should not be interactive

The build_release_candidate.sh script takes a long time to run. That means it is going to be in another tab or a person will (or anyhow SHOULD) walk away while it runs. It is very inefficient that it has interactive prompts that stop it completing.

It asks a few interactive questions at the beginning. This is OK but they could even more easily be command line flags.

Later there's y/n questions and can even be gpg interactions while it is running. They should all be noninteractive. The gpg key can be unlocked before launch by signing a dummy file.

Imported from Jira [BEAM-6599](https://issues.apache.org/jira/browse/BEAM-6599). Original Jira may contain additional context.
Reported by: kenn.