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/CommandLine.ts

@@ -37,6 +37,11 @@ export default class CommandLine {
     // Convert the string log level back to LoggingLevel enum
     const logLevel = rawOptions.logLevel ? LoggingLevelMapping.convertLoggingLevelTypeToLoggingLevel(rawOptions.logLevel) : defaultLogLevel;
 
+    // Validate required options are present
+    if (!rawOptions.applicationId || !rawOptions.secret || !rawOptions.pcastUri || !rawOptions.channelUri) {
+      throw new Error('Missing required command line options: applicationId, secret, pcastUri, and channelUri are required');
+    }
+
     return {
       ...rawOptions,
       logLevel