remove the required flag from the success metric for Goals Merged

We are trying to use a combination of Goals and initiatives to align to our OKRs for the company. because of how roadmap hierarchy reports work we need to define objective as a goal and KRs as initiatives for the report to work. right now our PMs have to put a - in the success metric because it is a required field. please remove this requirement so we can just set the name of the goal and thats it.