add the capacity to parse a JSON Object or JSON Array as a string in HTTP source plugins

[VictorD-Veolia]

Some APIs might return JSON data with dynamically changing schema for some fields. Today, HTTP Source plugins are not able to handle this kind of data.

For example, in the following google API , the field 'customSchema' might have a changing schema.

This pull request add the capacity to parse a JSON object/array to a stringify value.

Here is an example :

Considering the following input data :

{
	"someField":"someValue",
	"customSchema":{
		"customInnerField1":"innerValue1",
		"customInnerField2":"innerValue2",
		"customInnerField3":"innerValue3"
	},
	"someObject":{
		"someId":"someValue",
		"someType":"someValue"
	}
}

Where 'customSchema' might contain a large and unknown number of 'customInnerField'.

With this new feature, the plugin can handle this data if the configuration field 'Authorize Parsing of Objects to String' is set to True, and the field 'customSchema' is defined as STRING in the output schema.

The output record would then be :

{
	"someField":"someValue",
	"customSchema":"{\"customInnerField1\":\"innerValue1\",\"customInnerField2\":\"innerValue2\",\"customInnerField3\":\"innerValue3\"}",
	"someObject":{
		"someId":"someValue",
		"someType":"someValue"
	}
}

[rmstar]

• Please create a Jira describing the feature and link to it here
• Please fix merge conflicts
• Please add a unit test