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/TestConfiguration.ts

@@ -1,4 +1,5 @@
 import type {CommandLineOptions} from './CommandLine';
+import {LoggingLevel} from '../logger/LoggingLevel';
 
 type ApplicationCredentials = {
   applicationId: string;
@@ -26,6 +27,7 @@ export default class TestConfiguration {
   private readonly _publishers: string[];
   private readonly _tests: string[];
   private readonly _browserstack: BrowserstackConfiguration;
+  private readonly _logLevel: LoggingLevel;
 
   constructor(commandLineOptions: CommandLineOptions) {
     this._applicationCredentials = {
@@ -43,6 +45,7 @@ export default class TestConfiguration {
     this._viewers = commandLineOptions.viewers;
     this._publishers = commandLineOptions.publishers;
     this._tests = commandLineOptions.tests;
+    this._logLevel = commandLineOptions.logLevel;
     this._browserstack = {
       enabled: commandLineOptions.useBrowserstack,
       local: commandLineOptions.useBrowserstackLocal,
@@ -74,4 +77,8 @@ export default class TestConfiguration {
   get browserstack(): BrowserstackConfiguration {
     return this._browserstack;
   }
-}
+
+  get logLevel(): LoggingLevel {
+    return this._logLevel;
+  }
+}