Proposal: Add the ability to Downgrade

[evan-forbes]

Similar to having the ability to specifiy an increment to the app version in the binary or a config, we should also have the ability to decrement the app version. This might already be mostly possible, but we should add tests if that's the case.

[evan-forbes]

to update the most recent thinking around this proposal, the app version should likely only incremented. The main reason being that downgrades would require any state migrations to be backwards compatible, which would require a rather insane amount of testing to have full confidence in. If a specific portion or entirety of an upgrade can be confirmed to be causing a specific regression, then the app version should be incremented to apply or revert those changes.