Initial CI config. Needs verification

The .gitlab-ci-yaml is the driver for the tests. It will run CI as long as there is a configured runner to run it on.

The before_script will ensure Miniconda is installed and will create a sub-environment to use for testing, deleting it if it already exists. It will install the packages required for testing, currently just libnetcdf for the ncgen binary.

You may need to tweak and futz a few things to get it working.

Let me know if you run into issues.