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/config/Browserstack/BrowserstackApi.ts

@@ -1,4 +1,4 @@
-import SupportedBrowser from './SupportedBrowser';
+import type {SupportedBrowser} from './SupportedBrowser';
 
 // Source: https://github.com/browserstack/api
 
@@ -10,16 +10,18 @@ export class BrowserstackApi {
     this._authorizationHeader = `Basic ${Buffer.from(`${username}:${accessKey}`).toString('base64')}`;
   }
 
-  public async getSupportedBrowsers(): Promise<SupportedBrowser[]> {
-    const endpoint = `${this._baseUrl}/browsers?flat=true`;
+  public async getListOfSupportedBrowsers(): Promise<SupportedBrowser[]> {
+    const requestPath = `${this._baseUrl}/browsers?flat=true`;
     const headers = {
-      Authorization: this._authorizationHeader
+      Authorization: this._authorizationHeader,
+      'Content-Type': 'application/json',
+      Accept: 'application/json'
     };
 
-    const response = await fetch(endpoint, {headers});
+    const response = await fetch(requestPath, {headers});
 
     if (!response.ok) {
-      throw new Error(`Failed to fetch BrowserStack supported browsers due to [ ${response.statusText}]`);
+      throw new Error(`Failed to fetch BrowserStack supported browsers due to [${response.statusText}]`);
     }
 
     return response.json() as Promise<SupportedBrowser[]>;