Add configurable default and parameter-based strategy selection for affiliation matching

[jrhoads]

Purpose

The purpose of this PR is to introduce a configurable default for the affiliation matching logic in the ROR API and allow users to explicitly choose between the single_search and multisearch matching methods via request parameters.

Approach

The logic in OrganizationViewSet has been updated to evaluate matching strategy based on a hierarchy:

1. Explicit request parameters (single_search or multisearch).
2. A global environment variable configuration (SINGLE_SEARCH_DEFAULT).
3. Fallback to the legacy multisearch behavior.

Key Modifications

• rorapi/settings.py: Added SINGLE_SEARCH_DEFAULT setting, controlled by an environment variable (defaults to False).
• rorapi/common/views.py: Updated the list method in OrganizationViewSet to check for matching parameters and the new configuration setting.
• rorapi/tests/tests_unit/tests_views_v2.py: Added a new test suite AffiliationDefaultMatchingTestCase to verify that the logic correctly identifies which matching function to call based on different settings and query parameters.

Important Technical Details

• The multisearch parameter now acts as an explicit override to force the legacy matching logic even if SINGLE_SEARCH_DEFAULT is enabled.
• The default behavior remains unchanged unless the environment variable SINGLE_SEARCH_DEFAULT is explicitly set to True.

Types of changes

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

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