Modified pretrained_models.yaml to contain model catalog information with description, primary site, and supported sites.

[mraoaakash]

Partial PR for addition of pre-trained model documentation to the pretrained_model.yaml file. Includes the addition of a new filed called catalog to each model yaml entry. The entry is structured in the following manner:

catalog:
        description: >
                multi-line 
                model description
        primary_site:  primary site that model is supported for (agnostic for site-agnostic or multi-site models)
        supported_sites: 
            - other
            - supported 
            - sites

Fields can be read nested and used for downstream filtering tasks as necessary.

NOTE: This is a partial PR and does not contain the complete set of catalog entries as it proved difficult to ascertain the required catalog entries for some models. Someone with more complete knowledge of some models would have to take up the completion of the remaining catalog entries.

Description, primary site, and supported sites:

• resnet34-idars-cimp
• resnet34-idars-cin
• resnet34-idars-tp53
• resnet34-idars-hm
• mapde-crchisto
• sccnn-crchisto

Description only:

• micronet-consep
• mapde-conic
• sccnn-conic
• nuclick_original-pannuke
• nuclick_light-pannuke