Content entry traverser

[Pavel910]

Changes

This PR adds better test data for Content Entry Traverser, and improves data normalization and storage.

• single value fields with children (object and dynamic zone) now correctly generate field path while traversing data
• falsy values are no longer skipped and will be visited (null, false, [], "")
• DZ input is now normalized on the GraphQL resolver level, before the input is passed to Webiny domain logic
• DZ StorageTransform plugin was removed, as it's no longer necessary. This also improved performance of get/list operations, since there's no more redundant data transformation when data is fetched from storage.
• CmsModelFieldToGraphQL plugin now supports an optional normalizeInput function on the manage endpoint, so individual fields can implement data normalization

How Has This Been Tested?

Jest test.