Enhance CommandLine and TestConfiguration for improved option validation and logging

* Added validation for required command line options in the `CommandLine` class to ensure necessary parameters are provided.
* Updated `TestConfiguration` to store and expose the logging level from command line options.
* Refactored `BrowserstackApi` to improve method naming and added content type headers for API requests.
* Changed `SupportedBrowser` type to be exported for better accessibility.
* Updated `Page` and `SubscribingPage` classes to use a consistent browser import and improved constructor parameters.

test/pages/Subscribing.page.ts

@@ -1,9 +1,9 @@
-import {$} from '@wdio/globals';
+import {browser as wdio, $} from '@wdio/globals';
 import Page, {PageOpenOptions} from './Page';
 
 export class SubscribingPage extends Page {
-  constructor(baseUri: string) {
-    super(baseUri);
+  constructor(baseUri: string, browser: typeof wdio) {
+    super(baseUri, browser);
   }
 
   get videoElement() {
@@ -13,4 +13,4 @@ export class SubscribingPage extends Page {
   public override async open(options?: PageOpenOptions): Promise<void> {
     await super.open(options);
   }
-}
+}