Draft: Proto-env: Valpha

Context

OT1H when developing the protocol, we sometimes need to add elements to the environment.
OTOH when we are about to release, we want the environment to be stable (as with everything around release time) and we want to avoid introducing a new environment (to avoid releasing a WIP environment).

This MR addresses this conflict. It does so by introducing a new protocol-environment: Valpha. An environment specifically made for ProtoAlpha. This environment is meant to be somewhat unstable, to be changeable at any time. When the a protocol is snapshot, the state of the environment can be snapshot as well and made into a stable version.

DONE:

• Env Valpha
• Proto alpha uses Valpha
• manifest support
• Check to prevent any other protocol to use Valpha

TODO:

• Fix tests that upgrade from alpha to demo and such??
• integrate environment snapshoting with protocol snapshoting
• split the commits

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