Add a Dockerfile for the cosmosdb-server service

[hectcastro]

This PR includes two distinct changes, but they're split across separate commits in case it isn't desirable to merge both at this time:

1. Add a Dockerfile that uses Node.js 12.x to install the necessary project dependencies to run cosmosdb-server within a container. In addition, add support to the server itself to gracefully shutdown when given a subset of UNIX signals (e.g., SIGINT, SIGTERM).
2. Within a separate GitHub Actions workflow, build and publish the project container image to Docker Hub using credentials provided to the GitHub Actions execution context (e.g., DOCKERHUB_USERNAME and DOCKERHUB_TOKEN).

Additionally:

• An instance of the GitHub Actions run publishing to azavea/cosmosdb-server can be found here.
• Testing can be accomplished using that same published container image via:

$ docker run --rm azavea/cosmosdb-server:hmc-docker-support
Ready to accept connections at [::]:45751
^CAttempting a graceful shutdown...
Existing connections closed. Exiting...

Fixes #33

[hectcastro]

To facilitate testing this workflow in GitHub Actions, this used to listen to pushes on a branch. Before opening the PR, I updated it specifically to listen to pushes on tags.

[hectcastro]

This step looks a little over-engineered, but was used because it was the recommended approach to annotating the container image to be published .

[hectcastro]

These credentials need to be supplied to the GitHub Actions execution context. This can be done at the GitHub repository level, or at the GitHub organization level:

• https://docs.github.com/en/free-pro-team@latest/actions/reference/encrypted-secrets#creating-encrypted-secrets-for-a-repository
• https://docs.github.com/en/free-pro-team@latest/actions/reference/encrypted-secrets#creating-encrypted-secrets-for-an-organization

[hectcastro]

This Dockerfile was heavily influenced by the existing WIP changes in master...ridhoq:docker.

[nkzawa]

Thank you for the PR and sorry for the delay. The PR looks great but it's not ready to merge because we don't have an official account on dockerhub yet. I'm asking if we can prepare one.

[hectcastro]

No worries! Happy to reengage whenever the DockerHub account gets created.