Change docker images to use Alpine

[danyi1212]

Change the existing Docker files to use Alpine instead of existing Debian

https://github.com/permitio/opal/blob/master/docker/Dockerfile

Requires thorough review and tests

[gemanor]

@danyi1212, can you please specify in detail what Requires thorough review and tests means? What are the exact steps someone should walk through, and what output should they attach to the ticket?

[ariyonaty]

Started to take a crack at this during the Tikal event.
Here's the commit diff showing the differences (and image size reduced by sizable margin).

Haven't had much time since to perform testing, but my procedure was:

1. Build updating alpine-based images (based on make docker-build-next
2. Forked the example policy repo
3. Export appropriate envvars and kick off run.sh

If you can elaborate/clarify the testing procedure, I can go through that to the best of my ability as well.