add 'installSuccess' flag to telemetry, cache misses if npm install fails (#12163)

* add 'installSuccess' flag to telemetry, cache misses if npm install fails

* fix typo

src/server/protocol.ts

@@ -2081,6 +2081,10 @@ namespace ts.server.protocol {
          * Comma separated list of installed typing packages
          */
         installedPackages: string;
+        /**
+         * true if install request succeeded, otherwise - false
+         */
+        installSuccess: boolean;
     }
 
     export interface NavBarResponse extends Response {