Adds multiple members to a specific user group.

This endpoint adds multiple members to a specific user group, simplifying the process of bulk membership management.</br></br>Key features include:</br></br>- Bulk addition support: Enables the addition of multiple members in a single request, simplifying and streamlining bulk management processes.</br>- Clear success messaging: Returns a 200 success code with a confirmation message indicating the successful completion of the requested action.</br>- Comprehensive error handling: Returns 400 and 404 error codes with clear descriptions when requests fail.</br>- Targeted data addition: Leverages the userGroupId parameter in the URL path to add new members to the specified user group, ensuring accurate and focused modifications for effective domain management.