[GOT-38] Scope a proposal for versioning the execution pipeline (code, spec, communication to validators)

[jsign]

We need to scope how backward-compatible protocol upgrades would work:

• In the validator.
• The spec should now start explaining which feature lives in which network version.
• Include network versioning in our docs.
• Have playbooks to know how to deploy a new version at a future point in time, and communicate to validators to update their node with enough time, etc.
• See if we want to include contract upgrades as part of network versioning and how this fits into the validator, SDKs, etc.

This will take a reasonable amount of work, and there're more things to figure out. The above points are a brain dump of obvious things. This will probably need multiple people participating in this design.

cc @brunocalza @sanderpick @carsonfarmer @joewagner

_GOT-38