Release TerriaMap using create-docker-context

[tephenavies]

Current TerriaMap ghcr.io/terriajs/terriamap releases take more than 2 hours to run various typescript and webpack builds on virtualised ARM. This PR switches those releases to use create-docker-context.js to install dependencies and build JS once on the current machine, then create the multi-arch docker image using those build artifacts and installed dependencies. Development dependencies also will no longer be shipped in our docker images as create-docker-context.js does not copy these.

• Add metadata option supporting docker/metadata-action tags and labels
• Update release process to use create-docker-context for smaller images and faster buildx builds

[pjonsson]

Does the Dockerfile in the root of this repository serve any purpose after this PR, or should it be removed?

[pjonsson]

It looks like my comments about users and permissions have been resolved, is this ready to be merged?