Find a clean way of managing & configuring releases of OpenGB registry

[NathanFlurry]

The registry should be released as a whole since modules are very intertwined (compared to NPM modules)

We currently pin a revision in OpenGB to mitigate breaking changes

Solutions

• Auto-generate registry version in backend.yaml so it's pinned (this is like nix-channel)
  • Do we use a git hash or a tag?
  • Do we use a tag that updates like nix-channel?
• Add a cleaner way of specifying the main registry version as a unique registry type
  • Don't like this because GitHub-native is clean
• Track main by default and yolo it
  • Much more likely we accidentally break everyone's code, let's not do this

Prior art

• nix-channel