RAD-71: Initial Association datamodel schema support.

[PaulHuwe]

As the title says.. this is an initial take on a schema for associations. This was based on the JSON code at the bottom of this box. I am opening this in draft PR to facilitate conversation. There is a question of if we would like to validate JSON association files or not.

{
"asn_type": "image",
"asn_rule": "candidate_Asn_Lv2Image_i2d",
"version_id": null,
"code_version": "0.16.2.dev16+g640b0b79",
"degraded_status": "No known degraded exposures in association.",
"program": "00001",
"constraints": "DMSAttrConstraint({'name': 'program', 'sources': ['program'], 'value': '001'})\nConstraint_TargetAcq({'name': 'target_acq', 'value': 'target_acquisition'})\nDMSAttrConstraint({'name': 'science', 'DMSAttrConstraint({'name': 'asn_candidate', 'sources': ['asn_candidate'], 'value': "\\('o036',\\ 'observation'\\)"})",
"asn_id": "o036",
"asn_pool": "r00001_20200530t023154_pool",
"target": "16",
"products": [
{
"name": "r00001036001_02101_0001_wfi_i2d",
"members": [
{
"expname": "r0000101001001001001_01101_0001_WFI01_cal.asdf",
"exptype": "science",
"exposerr": "null"
},
{
"expname": "r0000101001001001001_01101_0002_WFI01_cal.asdf",
"exptype": "science",
"exposerr": "null"
},
{
"expname": "r0000101001001001001_01101_0003_WFI01_cal.asdf",
"exptype": "science",
"exposerr": "null"
},
{
"expname": "r0000101001001001001_01101_0004_WFI01_cal.asdf",
"exptype": "science",
"exposerr": "null"
},
]
}
]
}

[WilliamJamieson]

Does the association have to be JSON? For consistency with the rest of the files maybe they should be yaml or asdf files (in this case adding a few extra things to the yaml would make it an asdf file).

[mairanteodoro]

Looking good to me.

[ddavis-stsci]

LGTM