public Mono<Long> countRelationshipGroupMembers(
            @Nullable Set<Long> ownerIds,
            @Nullable Set<Integer> groupIndexes) {
        return userRelationshipGroupMemberRepository.countMembers(ownerIds, groupIndexes);
    }
@return true if added a new related user to the relationship group.
@implNote We call this method while upserting a relationship into the owner's relationship
          group in a transaction currently, so we don't check whether the owner has a
          relationship with the related user in this method.
turms-service/src/main/java/im/turms/service/domain/user/service/UserRelationshipGroupService.java