Provide Dockerfile with GDAL Base Image

**Is your feature request related to a problem? Please describe.**
Some Stetl apps need the latest/greatest GDAL and PROJ versions. For example [NLExtract](https://nlextract.nl) needs the GDAL/OGR [LVBAG Driver](https://gdal.org/drivers/vector/lvbag.html) which is now under active development. Debian (as Dockerfile is based on) and to some extent Ubuntu usually has older GDAL versions.

**Describe the solution you'd like**
Derive the Stetl Docker Image from a GDAL Base Image. We can start with separate Stetl `Dockerfile.gdal` and Image as not to disturb existing Stetl apps. Making a `Dockerfile.gdal` and tagging like `geopython/stetl:latest-gdal`,
`geopython/stetl:2.1-gdal3.2.2` etc. That way projects can gradually migrate. Finally we should aim for a single Stetl `Dockerfile`.

The [GDAL Docker Images](https://registry.hub.docker.com/r/osgeo/gdal) are very cleverly (with staging) built (by the GDAL author) and small, includes Proj , Python bindings and GDAL commandline tools. Also Stetl e.g. GML pipelines can benefit from latest GDAL/OGR (performance) enhancements.

**Describe alternatives you've considered**
Could have custom GDAL compilation in existing `Dockerfile` but is a complicated build chain will lead to long build times and maintenance issues.