Add CLI arg for starting without Brave Rewards extension

    Fixes #1103

    Related: #431

    You can do this with:

    ```
    npm run start -- --disable_brave_rewards_extension
    ```

    or

    ```
    yarn start --disable_brave_rewards_extension
    ```

build/commands/lib/start.js

@@ -19,6 +19,9 @@ const start = (buildConfig = config.defaultBuildConfig, options) => {
   if (options.disable_brave_extension) {
     braveArgs.push('--disable-brave-extension')
   }
+  if (options.disable_brave_rewards_extension) {
+    braveArgs.push('--disable-brave-rewards-extension')
+  }
   if (options.disable_pdfjs_extension) {
     braveArgs.push('--disable-pdfjs-extension')
   }

build/commands/scripts/commands.js

@@ -65,6 +65,7 @@ program
   .option('--user_data_dir_name [base_name]', 'set user data directory base name to [base_name]', 'brave-development')
   .option('--no_sandbox', 'disable the sandbox')
   .option('--disable_brave_extension', 'disable loading the Brave extension')
+  .option('--disable_brave_rewards_extension', 'disable loading the Brave Rewards extension')
   .option('--disable_pdfjs_extension', 'disable loading the PDFJS extension')
   .option('--ui_mode <ui_mode>', 'which built-in ui appearance mode to use', /^(dark|light)$/i)
   .option('--enable_brave_update', 'enable brave update')