Add support for wrapping PostgreSQL JSON queries

[EspadaV8]

I'm currently using https://github.com/darrylkuhn/dialect along side this package to better support the JSON columns in PostgreSQL, however, relationships on an external model to a model that has a JSON column fail because of incorrect wrapping of the JSON operators, e.g.

Undefined column: 7 ERROR:  column jobs.data->>'unit_id' does not exist

select * from "jobs" where "jobs"."data->>'unit_id'" = 2657 and "jobs"."data->>'unit_id'" is not null

The fix for that is in the wrapValue method and simply extends what's already there for the hstore wrapping.

Once that was fixed, there's another error when checking is null and is not null

Undefined function: 7 ERROR:  operator does not exist: jsonb ->> boolean

select * from "jobs" where "jobs"."data"->>'unit_id' = 2657 and "jobs"."data"->>'unit_id' is not null

The fix for this is to wrap the column and key within brackets

select * from "jobs" where "jobs"."data"->>'unit_id' = 2657 and ("jobs"."data"->>'unit_id') is not null

[mirzap]

Thanks.