Github action to build Relay to Github Package

[oracularhades]

Builds the Relay to a Docker Github package. The action is set to "on: workflow_dispatch", which is manual. I left out "on X" so a team member can set the condition.

This action file can also be used elsewhere!: "# To use this Github action file with another part of this repo, or with another project, change the DOCKERFILE and PACKAGE_NAME variables below.

🦋

Thanks, Josh.