added ability to set grid authorization type field to CurationTask

[andrewelamb]

Problem:

Curation grid sessions could only be created with the default authorization behavior, where the user who creates the session becomes its owner (SESSION_OWNER). There was no way to:

• Configure a CurationTask to recommend a particular authorization mode for the grid sessions opened against it.
• Create a Grid session with SOURCE_BENEFACTOR authorization, which lets anyone with EDIT permission on the source data collaborate in the same session without being added to a shared ownership team.

The affected code is the curation/grid model layer (synapseclient/models/curation.py) and the curator extension task helpers, which previously had no concept of an authorization mode.

Solution:

Added support for the grid authorizationMode field throughout the curation/grid models:

• Introduced a new AuthorizationMode enum (SESSION_OWNER, SOURCE_BENEFACTOR) mirroring the Synapse REST AuthorizationMode type, exported from synapseclient.models.
• Added a suggested_authorization_mode field (plus the not-yet-active collaborator_principal_ids) to FileBasedMetadataTaskProperties and RecordBasedMetadataTaskProperties.
• Added an authorization_mode field to Grid and CreateGridRequest, and wired it through create_async / to_synapse_request so it is sent at session-creation time and populated back from the response.
• When a CurationTask creates a new grid session, it now forwards task_properties.suggested_authorization_mode to the Grid.
• The curator extension task helpers (file_based_metadata_task.py, record_based_metadata_task.py) accept and pass through the suggested authorization mode.

Design notes / side effects:

• to_synapse_request for the task properties was switched to build a full dict and then strip None keys via delete_none_keys, instead of conditionally adding keys.
• owner_principal_id is now coerced to int when populated from API responses, fixing a type inconsistency.
• Documentation was updated in the metadata curation guide and the curator API reference pages.

Testing:

• Added unit tests verifying that CurationTask passes the correct authorization parameters when creating a grid session, and that the task properties / grid serialize and deserialize authorizationMode correctly (tests/unit/synapseclient/models/async/unit_test_curation_async.py, tests/unit/synapseclient/extensions/unit_test_curator.py).
• Added integration tests covering the new authorization mode behavior for grids and curation tasks (tests/integration/.../models/async/test_grid_async.py, test_curation_async.py).