[v4.0] Restrict top-level design space types.

[anoto-moniz]

Only product and hierarchical design spaces are allowed as the top-level design space type. Any top-level formulation or data source design spaces that remain on the platform can no longer be read by the SDK. Additionally, support for enumerated design spaces has been dropped entirely. All such design spaces will eventually be removed from the platform.

PR Type:

• Breaking change (fix or feature that would cause existing functionality to change)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Maintenance (non-breaking change to assist developers)

Adherence to team decisions

• I have added tests for 100% coverage
• I have written Numpy-style docstrings for every method and class.
• I have communicated the downstream consequences of the PR to others.
• I have bumped the version in __version__.py