This PR introduces comprehensive integration tests for the User Sharing API, ensuring correctness in user sharing, unsharing, and verification through a successful GET request for a user's shared organizations and assigned shared roles to a shared user in a given organization. These tests validate request handling, response accuracy, and expected behavior across various valid and invalid scenarios, ensuring API reliability in standard usage.

Test Coverage:

✅ Successful Scenarios

1. Selective User Sharing:
   • Covers single and multiple users across multiple organizations.
   • Validates all selective resource-sharing policies:
     • SELECTED_ORG_ONLY
     • SELECTED_ORG_WITH_ALL_EXISTING_CHILDREN_ONLY
     • SELECTED_ORG_WITH_ALL_EXISTING_AND_FUTURE_CHILDREN
     • SELECTED_ORG_WITH_EXISTING_IMMEDIATE_CHILDREN_ONLY
     • SELECTED_ORG_WITH_EXISTING_IMMEDIATE_AND_FUTURE_CHILDREN
2. General User Sharing:
   • Covers single and multiple users.
   • Validates all general resource-sharing policies:
     • ALL_EXISTING_ORGS_ONLY
     • ALL_EXISTING_AND_FUTURE_ORGS
     • IMMEDIATE_EXISTING_ORGS_ONLY
     • IMMEDIATE_EXISTING_AND_FUTURE_ORGS
3. General User Unsharing:
   • Covers single and multiple users.
4. Selective User Unsharing:
   • Covers single and multiple users.
   • Covers single and multiple organizations.

❌ Failure Scenarios

1. Selective User Sharing:
   • Selective User Sharing with invalid roles (single and multiple invalid roles).
   • Selective User Sharing with invalid organizations (single and multiple invalid organizations).
   • Selective User Sharing with invalid users (single and multiple invalid users).
   • Selective User Sharing with conflicting users (user exists in a child organization under the same username).
   • Selective User Sharing with non-immediate child organizations.
2. General User Sharing:
   • General User Sharing with invalid roles.
   • General User Sharing with invalid users.
   • General User Sharing with conflicting users.
3. General User Unsharing:
   • General User Unsharing with invalid users (single and multiple invalid users).
4. Selective User Unsharing:
   • Selective User Unsharing with invalid users and invalid organizations (single and multiple cases).
5. Selective User Re-Sharing:
   • Invalid Selective User Re-sharing (a shared user from a parent org cannot be re-shared from a child org).
6. General User Re-Sharing:
   • Invalid General User Re-sharing (a shared user from a parent org cannot be re-shared from a child org).

Related Issue

Add Integration Tests for User Sharing API #23328