feat(config): add support for disabling OpenAI compatibility providers

- Introduced a `Disabled` flag to OpenAI compatibility configurations.
- Updated routing, auth selection, and API handling logic to respect the `Disabled` state.
- Extended relevant APIs, YAML configurations, and data structures to include the `Disabled` field.
- Adjusted all relevant loops and filters to skip disabled providers.

Closes: #3060 #3059 #2977

internal/util/provider.go

@@ -98,6 +98,9 @@ func IsOpenAICompatibilityAlias(modelName string, cfg *config.Config) bool {
 	}
 
 	for _, compat := range cfg.OpenAICompatibility {
+		if compat.Disabled {
+			continue
+		}
 		for _, model := range compat.Models {
 			if model.Alias == modelName {
 				return true
@@ -123,6 +126,9 @@ func GetOpenAICompatibilityConfig(alias string, cfg *config.Config) (*config.Ope
 	}
 
 	for _, compat := range cfg.OpenAICompatibility {
+		if compat.Disabled {
+			continue
+		}
 		for _, model := range compat.Models {
 			if model.Alias == alias {
 				return &compat, &model