Generate docstring documentation using mkdocstrings

[jwestw]

We need to create technical documentation, automatically generated by mkdocstrings as it was by Spinx.

The pages should be generated under the DEVELOPER GUIDANCE section, under the title "Technical Documentation"

[jwestw]

I have created a branch for this (linked) and work is going well. I have created pages for most of the modules, but not the nested ones (e.g. src/time_table/SDG....) the auto docs generator doesn't pick up on the code I am using in the md file, like:

::: src.time_table.SDG_train_timetable

Here is the geospatial mods page open

I will push WIP