Support copying of JSON data to pubsub topic as JSON instead of stringified map.

Problem: The issue is with the sink connector, If schema is not used, JSON data in topic is pushed to pubsub topic as string value of the map.
We need a feature so that we can force the output to be JSON and could be interpreted as JSON in pubsub.

Example for JSON object
{"name":"bob","id":45}

it is shown as on pubsub topic
{name=bob, id=45}

Add a configuration which could be used to force output to be JSON.

Alternativies considered:
Tried forcing the output to be string using configuration
value.converter=org.apache.kafka.connect.storage.StringConverter

pubsub topic gets the right value but the single message transforms didn't not work, for example if you want to copy json field to header, it does not work.

Example: Sample SMT

"headers.publish" : true,
"transforms": "insertAppIdHeader,moveFieldsToHeader",
"transforms.moveFieldsToHeader.type": "org.apache.kafka.connect.transforms.HeaderFrom$Value",
"transforms.moveFieldsToHeader.fields": "name,id",
"transforms.moveFieldsToHeader.headers": "name,id",