chore: Migrate containers to informalsystems repos

[p-offtermatt]

Description

Closes: #1016

This PR removes the dependencies in the Dockerfile that point to my personal Dockerhub account.
Instead, the containers are now in the github container registry.
They are also tagged by version, so that it is easier to tell with what version the images are compatible.

The change in the start-chain script is to work with this new version of CometMock, where
the abci transport medium can now be chosen between grpc and socket, thus the command now has grpc as its last argument.

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