Additional Support of Models input

Models gives a brief overview on including the Models to the DL4 datasets.

The list of associated Models can be provided by -

1. Using models defined in Gammapy

   The list of Models used in Gammapy can be seen in Model Gallery.

   Additional models following the Gammapy standards, are defined in asgardpy.data.target module: Classes, and to use these models, one needs to invoke that module.

2. Using a list of models written in a different way than the Gammapy standard

   The module read_models and interoperate_models are used to read such models, for e.g. XML model definitions used by Fermi-LAT.

   A test covering all of these models is included in asgardpy, using a test xml file, included in the additional test data.

3. Using a Catalog available in Gammapy

   This is done by adding information in use_catalog. The list of available catalogs in Gammapy is documented at Source Catalogs

4. Using FoV Background Model as defined in Gammapy

   To add a default Gammapy FoVBackgroundModel to the 3D dataset, use add_fov_bkg_model = True.

   One can also include it in the config file by defining its spectral and/or spatial model components.