Publish snapshots through GitHub Actions

[echeipesh]

Circle CI is not longer cool. It would be great to manage releases from GitHub Actions, let us start by handling SNAPSHOTs first.

[pomadchin]

@echeipesh https://github.com/sbt/sbt-ci-release; + https://github.com/locationtech/geotrellis/blob/master/.github/workflows/ci.yml#L39-L66 for the Scala part is the easiest way:

Basically setting a couple of secrets and adding a generic publish step + adding plugin.

Good question what creds do we need to set for the Py artifacts release.