Automate the release process

[erwanor]

Feature Summary

Cutting new releases of the ibc-rs and ibc-proto-rs crates should be as simple as creating a new semver tag on main.

Proposal

• simplify the "Release" section of CONTRIBUTING (remove as many manual steps as possible)
• create a release.sh script
• create a Release-ready workflow that hints reviewers as to whether a new release PR is "ready"
• create a Release workflow that handles deploying on crates.io
  • give rights to @bftbot to publish the ibc-rs and ibc-proto-rs crates
  • add CRATES_TOKEN (crates.io API) to the repo's secrets

[erwanor]

Hey @plafer, following our discussion in #461 -- note that a lot of those already exist thanks to Thane's work in tendermint-rs, so my PR will focus on getting them here as well, and future work will refine the ergonomics of cutting releases (e.g. checking that unclog has been properly ran etc.)