Allow to define the path of the shell in app preferences (#2194)

Co-authored-by: Sebastian Malton <sebastian@malton.name>

src/common/user-store.ts

@@ -20,6 +20,7 @@ export interface UserStoreModel {
 
 export interface UserPreferences {
   httpsProxy?: string;
+  shell?: string;
   colorTheme?: string;
   allowUntrustedCAs?: boolean;
   allowTelemetry?: boolean;