Nested Primary keys and Incremental keys in data is a pain

When data has a primary key but it's nested in an Object the Singer spec itself doesn't tend to work well. We resort to doing something like https://github.com/AutoIDM/tap-googleads/pull/28 which means we create a field like _sdc_primary_key at the top level so that key_properties in the schema can reference the proper field (nested objects don't work)

This was brought up here https://meltano.slack.com/archives/C01PKLU5D1R/p1649947327618639 , and I thought randomly of using a jsonpath to point to your key_properties instead would be nice!

@edgarrmondragon had an idea from that! So here we go :D