Add proxy support to feature flag fetching

Feature flag fetching was also missing proxy support like telemetry
exporter was. Applied the same fix:

- Get HTTP agent from connection provider
- Pass agent to fetch call for proxy support
- Follows same pattern as CloudFetchResultHandler and DBSQLSession
- Supports http/https/socks proxies with authentication

This completes proxy support for all HTTP operations in the telemetry
system (both telemetry export and feature flag fetching).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: samikshya-db

lib/telemetry/FeatureFlagCache.ts

@@ -127,14 +127,19 @@ export default class FeatureFlagCache {
 
       logger.log(LogLevel.debug, `Fetching feature flags from ${endpoint}`);
 
-      // Make HTTP GET request with authentication
+      // Get agent with proxy settings (same pattern as CloudFetchResultHandler and DBSQLSession)
+      const connectionProvider = await this.context.getConnectionProvider();
+      const agent = await connectionProvider.getAgent();
+
+      // Make HTTP GET request with authentication and proxy support
       const response = await fetch(endpoint, {
         method: 'GET',
         headers: {
           ...authHeaders,
           'Content-Type': 'application/json',
           'User-Agent': `databricks-sql-nodejs/${driverVersion}`,
         },
+        agent, // Include agent for proxy support
       });
 
       if (!response.ok) {