Write files in `etc` directories as Python files

[NParsonsMO]

Write the files in the etc directories as Python files:

• app/configure_for/etc/recipe_paths.yml (although this may be removed following Remove fetch_recipe.py #514)
• app/configure_standardise/etc/request_defaults.yml
• app/configure_standardise/etc/streams.yml

Proposal:

• Create a config.py module in each app's bin directory
• Add the contents of the yml files to the config.py module as dictionaries, such that the imports are:
  • from config import recipe_paths
  • from config import request_defaults
  • from config import streams
• When cmewpy is created, only the imports will need updating to e.g. from configure_for.config import recipe_paths (in the same way as all the other Python modules) 👍