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/api/handlers/management/api_tools.go

@@ -766,6 +766,9 @@ func resolveOpenAICompatAPIKeyProxyURL(cfg *config.Config, auth *coreauth.Auth,
 
 	for i := range cfg.OpenAICompatibility {
 		compat := &cfg.OpenAICompatibility[i]
+		if compat.Disabled {
+			continue
+		}
 		for _, candidate := range candidates {
 			if candidate != "" && strings.EqualFold(strings.TrimSpace(candidate), compat.Name) {
 				for j := range compat.APIKeyEntries {