Publish SimApp Docker image to GHCR

[rootulp]

Context

#70 and #48

Problem

I tried adding a GitHub action to build and push a SimApp Docker image but it fails with a 403.

Proposal

Identify why the GitHub action can't publish a Docker image to GHCR and resolve. cc: @MSevey

[rootulp]

Note in the meantime it is still possible to build and publish a SimApp Docker image using the make commands: make build-simapp-docker and make publish-simapp-docker.

[MSevey]

I added the .github repo with write access to the packages. This solved perms issues in the past for me.
LMK if this resolves the issue.

[rootulp]

Thanks! Will retry

[rootulp]

https://github.com/celestiaorg/celestia-zkevm-ibc-demo/actions/runs/13551771119/job/37876803658 👀

failed: https://github.com/celestiaorg/celestia-zkevm-ibc-demo/actions/runs/13551771119/job/37876817865#step:8:1896

given this is a low priority issue, not investigating now