scripts/proto_manager.sh: rehash a protocol

What

Add an automatic rehash command to proto_manager. It rehashes any protocol_source given in parameter and updates other parts of the repository accordingly. In case of a beta rehash it mostly simply replace the hash everywhere it is needed, for a rehash of a snapshotted protocol (for instance to prepare a UAU or an alternative proposal) it also updates the protocol directory and associated links in other files.

Why

How

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR