[770] handle arrays of JSON-friendly objects

[misaka]

We've previously added special handling to event data processing for objects that can be converted to JSON; this change expands that to handle an array of these objects that can be converted to JSON. Words are hard, a pictureJSON structure is worth a thousand words:

BEFORE BAD:

        {
          "key": "accrediting_provider_enrichments",
          "value": [
            {
              "UcasProviderCode": "N21",
              "Description": "",
              "validation_context": null,
              "errors": {
              }
            }
          ]
        }

NOW GOOD:

        {
          "key": "accrediting_provider_enrichments",
          "value": [
            "{\"UcasProviderCode\":\"N21\",\"Description\":\"\",\"validation_context\":null,\"errors\":{}}"
          ]
        }

(we now encode each element of the array to JSON).

This has change has also been tested in the test environment.

[misaka]

cc: @avinhurry for the assist