Split config-developer.yml

[stefsmeets]

Is your feature request related to a problem? Please describe.
I would like to start a discussion about reorganizing or splitting config-developer in a few better defined configuration files/settings.

I suggest to make the config-developer's only responsibility to defining the location of data. Currently the config-developer feels a bit overloaded with all sorts of keywords without a clear place to go. We could split off the institutes and cmor configuration (these are only read in when loading the CMOR tables). We think this will lead to a better separation of concerns, and make maintaining/modifying the config-developer simpler.

For example, we could have:

• esmvalcore/cmor/cmor_config.yml
  This file will be read in by cmor.table.load_cmor_tables. For those who want to override the cmor settings, we could add a new setting in the config-user.yml to define the path to a custom file, i.e. cmor_config: path/to/cmor_config.yml.
• esmvalcore/cmor/institutes.yml
  The institutes are also only read in by cmor.table.load_cmor_tables which are only relevant for the CMIP3/CMIP5, but currently comprise half the number of lines in config-developer.yml. It would be simpler to have these in their own file, and define a new settings for those who want to update it.
• esmvalcore/config-developer.yml
  Stays as it is, but with institutes/cmor settings moved.

Would you be able to help out?
👍