Geographical 2D plots fail without internet access

### Describe the bug
Geographical 2D plots try to load the coastlines from the internet. If the host does not have connection to the internet it will crash the whole bake_recipe task in the workflow. Note that this is important as some of the current HPC installations have internet access restrictions from some hosts (i.e. EarthSciences New Zealand (former niwa) has internet access blocked on compute nodes, preventing us from using a large pool of resources and harming scalability).

### How to reproduce

Steps to reproduce the behaviour:

1. It is installation dependent, so to reproduce you will need to find a server that doesn't have access to the internet
2. Run cset-workflow with a recipe that runs geographical 2D plots
3. The `bake_recipe` task should fail with a https socket error visible in any of the `bunch.*.err`
4. Note that at NCMRWF, running the workflow once in a server with access to the internet, allowed to run it later (same user, same workflow, another run id) from a server without internet access, but still fails for other users using the same environment the first time they run if the server doesn't have internet access. This is a behaviour that I don't fully understand.

### Expected behaviour
It should work from any host, probably trying first to run with high-quality coastline that require internet access, and if that fails use lower quality coastlines that are installed as part as the cset environment.