Resolve "Ai::ServiceAccountMemberAddService fails to add service account user"

What does this MR do and why?

I wasn't able to replicate the issue mentioned in #565863 (closed) but figured I would at least make the code a bit more defensive. This MR prevents potential crashes if the add operation fails completely and returns nothing, making the service more robust by handling both partial and complete failures.

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Related to #565863 (closed)