ci: relayer container build

[conorsch]

Towards #465. Here we define a container image that wraps the upstream cosmos/relayer image with the custom scripting for bootstrapping clients on the Penumbra testnet and preview networks. No other chain configs are part of this container image as of yet. The container image will be publicly available as ghcr.io/penumbra-zone/relayer. It isn't yet deployed to the cluster: that'll come next.

[conorsch]

The build action for the new relayer container was initially failing. Turns out there was a conflicting package with the same name in our GH, due to our fork of the relayer repository, and its automatic use of the repo name in its package creation: https://github.com/penumbra-zone/relayer/blob/9c7e897777d5d7843dfad2ba169cedff2eff775a/.github/workflows/docker-publish.yaml#L12

To resolve, I downgraded that repo's privileges on the GH package to "read", and elevated this repo's privs to "admin." On a subsequent rerun, the build worked, and I'm able to pull it locally now:

❯ docker pull ghcr.io/penumbra-zone/relayer:main
Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
Trying to pull ghcr.io/penumbra-zone/relayer:main...
Getting image source signatures
Copying blob bd9c25980e10 done  
Copying blob 4ed5f2fb37e2 skipped: already exists  
Copying blob 86b39e51d0be done  
Copying blob f97a99d8b7c1 done  
Copying blob bd355b9fa562 done  
Copying blob ab56602a6b2b done  
Copying blob 4f4fb700ef54 skipped: already exists  
Copying blob 48ec50bfcec3 done  
Copying config 79257117ba done  
Writing manifest to image destination
Storing signatures
79257117ba783f5819e51dd771ad623356add186e31b0914f67ce7d76abd8f45