Use dynamic walk for validating unique resource identifiers

[shreyas-goenka]

Changes

Using dynamic walk here removes the need to add validation when a new resource type is added. All resources will be automatically validated to have unique keys.

Tests

Modified existing unit tests and added new ones.

[shreyas-goenka]

Note: https://github.com/databricks/cli/pull/1425 will add a test to assert resources are maps of string -> pointers to a struct.

[shreyas-goenka]

Closing in favour of https://github.com/databricks/cli/pull/1614