[DAR-3771][External] Import of annotation-level properties

[JBWilkie]

Problem

darwin-py is currently incapable of handling:

• 1: A per-property granularity field in the .v7/metadata.json properties manifest file
• 2: frame_index=null values for annotation-level property values

Both concepts must be supported by darwin-py to allow the same import functionality as section-level properties (which are currently supported properties)

Solution

• Extend the Property class with granularity
• Introduce the PropertyGranularity enum to represent the 3 property granularities

Adjusted the properties import functions to ensure :

1. Annotation-level property values can be imported, but that granularity is optional so that section-level property values can still be imported
2. Annotation-level property values present in the properties manifest but that are missing in the team can be created in the team
3. Annotation-level properties present in the properties manifest but that are missing in the team can be created in the team

We also add unit tests for _import_annotations, as none previously existed. These test that for both section & annotation-level properties:

• Existing property values can be imported as expected
• New property values can be created from the manifest file
• New properties themselves can be created from a manifest file, and section-level properties can still be created without specifying a granularity

Changelog

Added support for annotation-level properties