new release process / CI actions / checks

[sam0x17]

We want to move to a more formal release process characterized by the following points:

• all PRs merge into main
• PRs don't get merged until they are finney-ready
• labels will be used to indicate that a PR is on-devnet, devnet-pass, on-testnet, and testnet-pass, respectively, and having both the devnet-pass and testnet-pass labels will be required by the CI to merge into main.
• any issues uncovered during testing can then be discussed and tracked on the PR, reducing issue/PR bloat and making it easy to see the full life-cycle of a feature from development to deployment on finney
• we will cut releases off of main using the github releases feature, so every once in a while we cut a new release and deploy everything new in main to finney, and then that gets a semver version number + tag
• also new github actions to run our (now manual) deploy process, these will include a built in check that the spec version has been bumped to a value higher than the net we are currently deploying to. If this criterion is not met, the deploy will abort, which will prevent issues like the recent testnet forking/bricking

all work in #346

AC:

• [x] CI check system for devnet / testnet stages (possibly using labels)
• [ ] github actions for deploys
• [ ] set up releases
• [ ] PRs default to main
• [ ] update docs / instructions / PR templates
• [ ] test that non-team-members can't fake the checklist items