Add a plethora of config options to a-b-c. (#1958)

Closes #1861 
Closes #1783 

- arbor-build-catalogue (a-b-c) does no longer need to be in a fixed location
- nor do we statically fix the configuration for a-b-c
- instead, we rely on `arbor.config` to read the relevant default values
- each value can be overriden, if desired
- added many more values to the configuration
  - gpu type and arch
  - paths and prefix 
  - CXX
- report default settings for better diagnosis
- implement a fallback for prefix if that does not exist; in particular for the amazing skbuild.

In essence you can now use a-b-c as a standalone tool, as long as you have a properly 
configured py-arbor.

Example output after removing `_skbuild`
```
Warning: prefix '/Users/hater/src/arbor/_skbuild/macosx-11.0-x86_64-3.10/cmake-install' does not exist, falling back to '/Users/hater/src/arbor/.direnv/python-3.10.6'.
usage: arbor-build-catalogue catalogue_name mod_source_dir

Generate dynamic catalogue and build it into ...