Add support for Generative Language API Key and improve client initialization

- Added `GlAPIKey` support in configuration to enable Generative Language API.
- Integrated `GenerativeLanguageAPIKey` handling in client and API handlers.
- Updated response translators to manage generative language responses properly.
- Enhanced HTTP client initialization logic with proxy support for API requests.
- Refactored streaming and non-streaming flows to account for generative language-specific logic.

internal/config/config.go

@@ -20,6 +20,8 @@ type Config struct {
 	ApiKeys []string `yaml:"api-keys"`
 	// QuotaExceeded defines the behavior when a quota is exceeded.
 	QuotaExceeded ConfigQuotaExceeded `yaml:"quota-exceeded"`
+	// GlAPIKey is the API key for the generative language API.
+	GlAPIKey []string `yaml:"generative-language-api-key"`
 }
 
 type ConfigQuotaExceeded struct {