define hazard_config for default models with a file

[chrisdicaprio]

"official" models are defined with this pattern:

model_args: Dict[str, Any] = dict(
    version='NSHM_v1.0.4',
    title="NSHM version 1.0.4, corrected fault geometry",
    slt_json="nshm_v1.0.4_v2.json",
    gmm_json="gmcm_nshm_v1.0.4.json",
    gmm_xml="NZ_NSHM_GMM_LT_final_EE_new_names.xml",
    hazard_config=copy.deepcopy(OpenquakeConfig(DEFAULT_HAZARD_CONFIG)),
)

For symmetry and cleaner typing, it would be nice to define the hazard_config with a file like the other parameters

requires ability to serialize/deserialize config objects #103

done when:

• serlialize / deserialize config objects #103
• models "NSHM_v1.0.0" and "NSHM_v1.0.4" have files in resources for their configs
• official model definitions use filepaths to the configs