This diff adds keyserver url validation logic to the onPressSave callback in the add keyserver screen. We also now display an error message if for any reason the keyserver url inputed by the user is not valid
Linear task: https://linear.app/comm/issue/ENG-4917/update-onpress-of-goadd-button-in-customservermodal-to-add-keyserver
Depends on D9666