Context

This MR makes a couple of changes in an attempt to fix #1966

Move constants into their own modules to represent current and previous, Constants_parametric_repr and Constants_parametric_previous_repr, respectively.
Add script to automatically update Constants_parametric_previous_repr with a specified protocol version's Constants_parametric_repr and clean up protocol migration code. There is currently a complete standalone script and an incomplete integration into snapshot_alpha.sh.

This is currently a draft since it is undecided if:

This is an approach we would like to take.
If the script should be integrated into snapshot_alpha.sh or be used as a standalone script (currently named copy_and_prepare_parametric_constants.sh).

Manually testing the MR

See !4580 (comment 867699735) for a way to test the standalone script.

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

Edited Mar 15, 2022 by metanivek