Have process plugins support json as input and output

[rouzier]

What do you want to change?

Example config

{
 "version": "2",
 "sql": [
{
 "schema": "schema.sql",
 "queries": "query.sql",
 "engine": "postgresql",
 "codegen": [
{
 "out": "gen",
 "plugin": "jsonb"
 }
 ]
 }
 ],
 "plugins": [
{
 "name": "jsonb",
 "process":{
 "cmd": "test_json_process_plugin",
 "format": "json"
 }
 }
 ]
}

What database engines need to be changed?

No response

What programming language backends need to be changed?

No response