Adding workflow to create feathr api/ui image nightly and for each release

[jainr]

This workflow builds the docker container for Feathr API/UI and publishes to dockerhub with appropriate tag It has two triggers,

1. nightly i.e. runs every night at 10 pm UTC
2. Anytime a new branch is created under releases example releases/v0.7.0

The final image in dockerhub would have following labels

[xiaoyongzhu]

per the doc here (https://docs.docker.com/ci-cd/github-actions/), looks like we should use actions such as docker/build-push-action@v2 rather than pinning it to a specific commit?

[jainr]

@xiaoyongzhu - Thanks for the review , removed reference to specific commits and checked that it works. https://github.com/jainr/feathr/actions/runs/2828455224