Handle External Member Invitation on the Profile MS

Issue 1

When a user is invited to a space or course owned by an organization, and they are not yet a member of that organization, they should be added as an external member upon accepting the invitation.
Currently, this behavior is not reflected in the IAM section until the invitation is accepted, and there is no automatic creation of the corresponding OrganizationMember document.

The goal of this task is to ensure that when the invitation to a course or space is created, the resulting "member invited" event is properly handled by the Profile microservice, which will then create the appropriate external OrganizationMember document.
This ensures that external members are correctly tracked and displayed under the "External Members" section in IAM.

Note: Spaces and courses are still using the old invitation endpoints. The FE should be updated to use the new invitation endpoints provided by the Membership MS to ensure full integration and consistency across the system.

Issue 2

When an external member is invited to the organization, the invitation is created properly but the user is not able to join the organization because it doesn’t receive the notification

https://sharing.clickup.com/clip/p/t9004002740/2b42a041-9564-436b-a67c-411bad30d0ce/2b42a041-9564-436b-a67c-411bad30d0ce.webm?filename=screen-recording-2025-07-25-15%3A23.webm