Use agoric's synchetic chain image

[toliaqat]

This PR utilizes the Agoric chain's mainnet synthetic chain Docker image from the Agoric-3-proposals repo, rather than replicating the Agoric chain build process. This image includes all the upgrade proposals made to the agoric mainnet.

Testing was conducted using the following commands.

./heighliner build -c agoric -g main
docker run -it --rm --entrypoint sh agoric:main

[ivanlei]

I've been able to use this successfully but needed to hand edit the agoric docker image to build from

[ivanlei]

@toliaqat - could this be turned into an ARG AGORIC_BASE_IMAGE such that someone could run something akin to:

heighliner build -c agoric -g main --build-env 'AGORIC_BASE_IMAGE="ghcr.io/agoric/agoric-3-proposals:myprivatetag"

[agouin]

Thanks for the PR @toliaqat ! We already have the imported dockerfile for this purpose however, which enables building on top of existing docker repository images. We actually built with that initially for agoric before we switched to build agoric from source. I think it would be better to switch agoric back to the imported dockerfile and extend the imported dockerfile if necessary than bring in an agoric specific dockerfile.

You can see in this PR #130 that we switched from the imported dockerfile to the build from source approach. We like to build from source wherever possible with heighliner, but importing from an existing registry is an approach we can consider also.