Get a list of itemGroupData object names

[chowsanthony]

Querying JSON can be done either using JSON Pointer (Published RFC) or JSONPath (Draft RFC).

JSON Pointer requires a predetermined path and does not support wildcards. Meanwhile, JSONPath is still evolving as a standard, and different vendors offer varying levels of wildcard support, or lack of.

It could be useful to have an endpoint that returns a list of itemGroupData object names. For example, it will return ['IG.CM'] from this file. In other words, $..itemData or $.referenceData.itemGroupData.*.itemData may not be well supported:

{
    "creationDateTime": "2023-06-28T15:38:42",
    "datasetJSONVersion": "1.0.0",
    "fileOID": "www.cdisc.org/StudyMSGv2/1/Define-XML_2.1.0/2023-06-28/cm",
    "asOfDateTime": "2023-05-31T00:00:00",
    "originator": "CDISC SDTM MSG Team",
    "sourceSystem": "Sponsor System",
    "sourceSystemVersion": "1.0",
    "clinicalData": {
        "studyOID": "cdisc.com/CDISCPILOT01",
        "metaDataVersionOID": "MDV.MSGv2.0.SDTMIG.3.3.SDTM.1.7",
        "metaDataRef": "https://metadata.location.org/CDISCPILOT01/define.xml",
        "itemGroupData": {
            "IG.CM": {
                "records": 68,