Add github workflow to build container images on repo tag

[spwoodcock]

Fixes #167

Issue

• A few users are requesting pre-built container images on GHCR, myself included 😄
• It's a low effort small win, to aid distribution of tippecanoe.

Solution

• Add a Github workflow to build the container image whenever a new tag is made on this repo.
• The image will be tagged and labelled to match the repo tag.
• The image will be multi-architecture: AMD64 + ARM64.

Note

If this PR is accepted, a small change could be made to the README referencing the images (instead of requiring the user to build themselves).

[bkeepers]

I set up an automated nightly docker build at https://github.com/openwatersio/tippecanoe. It has the latest version and going forward it will build any new releases.

docker pull ghcr.io/openwatersio/tippecanoe