Allow filter by fields

[baubakg]

We should be able to fetch a specific value from the result payload. This is either the result field or a method.

Currently

Call

{
	"callContent": {
		"fetchString1": {
			"class": "com.adobe.campaign.tests.bridge.testdata.one.MimeMessageMethods",
			"method": "createMessage",
			"args": [
				"mre"
			]
		}
	}
}

Result

We get a lot of values:

{
	"callDurations": {
		"fetchString1": 15
	},
	"returnValues": {
		"fetchString1": {
			"messageNumber": 0,
			"size": -1,
			"subject": "a subject by me mre",
			"hashCode": 370140205,
			"isExpunged": false,
			"contentType": "text/plain",
			"content": "a content by yours truely mre",
			"lineCount": -1
		}
	}
}

Expected

We should be able to extract / filter the result to a certain depth

Rationale:

Example: if we want to use the subject in a different call, and there is no getter, and it may be a bit large.