Task packaging as container image.

[trulede]

This is a dockerfile and workflow for distributing Task in a scratch based image. Images would be pushed to GHCR, which is significantly less a pain in the arse than pushing images to Docker Hub, but you can do that too ... I doubt its worth the effort!

Workflow integration is tedious, the example I have provided should work out-of-the-box.

edit: ... however, the workflow should probably be triggered after all other checks have occured, which is to say ... after the normal release process has completed (and binaries are published).

fixes #1801

[trulede]

This is an alternative to #1875 (and #1868?) and just simply distributes task in a container. People can use this image in a multi-stage build to directly install the task binary and avoid compilation delay of manually installing task. And also to pin versions.

Generally, running task in a container provided by go-task is not itself useful, since: we (royal "we") are not going to trust that image (at all!); we put a lot of effort into our own images; and in any case we need to package additional tools which task itself is then automating. Also, providing docker images for broad distribution is a lot of stuffing around ...

Therefore this alternative is provided.