Fix non-null violation when inviting people to team (#3015)

### What problem does this PR solve?

Not sure why MySQL is inserting empty string in this case, but when I
use postgres I got `null value in column "invited_by" of relation
"user_tenant" violates not-null constraint`

### Type of change

- [X] Bug Fix (non-breaking change which fixes an issue)

api/apps/tenant_app.py

@@ -57,6 +57,7 @@ def create(tenant_id):
         id=get_uuid(),
         user_id=user_id,
         tenant_id=tenant_id,
+        invited_by=current_user.id,
         role=UserTenantRole.INVITE,
         status=StatusEnum.VALID.value)
 
@@ -95,4 +96,4 @@ def agree(tenant_id):
         UserTenantService.filter_update([UserTenant.tenant_id == tenant_id, UserTenant.user_id == current_user.id], {"role": UserTenantRole.NORMAL})
         return get_json_result(data=True)
     except Exception as e:
-        return server_error_response(e)
+        return server_error_response(e)