Make notebooks domain agnostic

[hsteptoe]

Currently the notebooks have a lot of hard-coded content that references SE Asia. We should aim to make the notebooks more agnostic to the input (CORDEX) data being used, so these notebooks feel more relevant to learners.

This issue is to discuss how we could do this. The major options are:

1. Create bespoke version of a principal repo, which is hard-coded to be specific to a set of learners.
2. Abstract file name, regions etc. into a top-level configuration file which can be edited by learners to tailor the main repo to their country/domain of choice.