This diff introduces the ADD_KEYSERVER redux action type as well as the AddKeyserverPayload type that we will need for this redux action. Since at this moment we are only adding and persisting any newly added keyserver to the keyserver redux store, we don't need start, success, fail action types since we are not making any calls to an endpoint
Linear task: https://linear.app/comm/issue/ENG-5339/introduce-addkeyserveractiontype
Depends on D9590