Add two additional containers to provide Previewers locally

[gschmutz]

What this PR does / why we need it:

This PR adds two additional docker containers:

• register-previewers - registers previewers in Dataverse
• previewers-provider - provides all previewers locally

Previewers to register can be included/excluded by using INCLUDE_PREVIEWERS or EXCLUDE_PREVIEWERS environment variable. If both are empty, then all previewers are installed.

You can list the available previewers by running docker run trivadis/dataverse-deploy-previewers:latest previewers.

If you don't run docker on the same machine, then set the MACHINE_IP environment variable to the IP-Address of the Docker host.

[pdurbin]

Works great!

I'm going to go ahead and merge this. Let's follow up with another pull request for to add this to docker-compose-dev.yml and add some docs.

Thanks, @gschmutz!