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/watcher/clients.go

@@ -357,6 +357,9 @@ func BuildAPIKeyClients(cfg *config.Config) (int, int, int, int, int) {
 	}
 	if len(cfg.OpenAICompatibility) > 0 {
 		for _, compatConfig := range cfg.OpenAICompatibility {
+			if compatConfig.Disabled {
+				continue
+			}
 			openAICompatCount += len(compatConfig.APIKeyEntries)
 		}
 	}