Additional sql db support array and json values

[iamkelllly]

To enable full support of SQL databases, Fidesops should:

• support an array of values in a field where fidesops loops through each array item in the field and searches for identity to add to identity graph and/or PII to access and mask.
• support a json object as a field value where fidesops scans each node and searches for identities to add to the identity graph and/or PII to access and mask.

[seanpreston]

This should feature a review of the different types of ways we can access array / object values across datastores. A feature matrix describing how array / object values are addressed would help here, so we can be clear about what is and is not supported.

@NevilleS has articulated the learnings from Atlas indicate that we should work on #94 first here as we'll want how we handle Mongo here to influence SQL instead of vice versa.