Picking up of colocated data objects should be tied to specific models

[lewisblake]

Describe the bug

The obs_only and coldata_dir used for an obs network can not handle multiple models as it stands. Maybe make coldata_dir into a col_datadirs dict in which the keys are model_id's and the values are the directories for those coldata dirs. Then a obs-network is associated to a specific model. Need this to compare the same obs network against multiple models.

• Pyaerocom version: v0.18.dev0
• Computing platform: Linux
• Configuration file (if applicable): /lustre/storeB/users/lewisb/Python/Evaluations/aeroval/config/config_files
• Error message (if applicable): NA

To Reproduce Steps to reproduce the behavior:

1. Run the config