Improve the experience to run a Postgres server with documentdb

[safern]

Currently the README suggests to build the devcontainer dockerfile, however a devcontainer is intended for development, more so for use within Visual Studio Code using their devcontainer features.

However, there are scenarios where people should be able to just build a dockerfile which does something like:

1. Base container is the shelf Postgres container
2. Pulls in documentdb (either from a tag/release)
   2.1 Builds documentdb and installs it
   2.2 Setups documentdb with the right configs to listen outside the port (maybe make this ARG configurable):
   - listen_addresses GUC
   - hba.conf file to allow connections from outside the container
3. Entry point starts postgres with documentdb

We should probably do this in 2 steps:

• Provide the dockerfile and update README for people to just do docker build + docker run.
• Publish a docker image into a public container registry for people to just do docker run with it.

cc: @visridha @lichoil @sivethe