Automatic Publishing of Docker Images To Git Registry

[mdvertola]

Issue #, if available: N/A

Description of changes:
Adding a github workflow that builds and uploads the gateway and gateway-ecs images on merges to main to the github container registry.

Important call-outs to this PR:

• since this repo does not appear to currently be using any versioning I configured to trigger on pushes/merges to main. For the same reason, i am tagging the images with the first several letters of their commit hash so they can be easily tracked to a point in time. (referred to as SHORT_SHA)
• we build two images on each merge to main: SHORT_SHA and SHORT_SHA-ecs
• can certainly be done with aws ecr but i figured this would be the shortest path to getting published container images as we will inherit github organization permissions to access the registry for upload vs managing aws credentials or docker credentials for ECR/DockerHub respectively.

Other:
if this is already published somewhere please add to docs! I luckily only took a short side step here to make this happen since i had a lot of the workflow file sitting around from other projects and know the eco system well but i am sure this could create a lot of friction/ poor DX for those not as familiar.

All in all though thanks for the work here in building this, seems to be a rock solid implementation and hope that the more i use it, the more I can contribute! Cheers to you guys for this.

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