feat: add Cosmo Router config generation and PubSub support

Creates a new `GenerateCosmoRouterConfig` function to build and 
serialize a Cosmo Router configuration from subgraphs. Implements 
PubSub mechanism for managing schema updates, allowing 
subscription to updates. Adds Subscription resolver and updates 
existing structures to accommodate new functionalities. This 
enhances the system's capabilities for dynamic updates and 
configuration management.

graph/cosmo.go

@@ -0,0 +1,54 @@
+package graph
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"gitlab.com/unboundsoftware/schemas/graph/model"
+)
+
+// GenerateCosmoRouterConfig generates a Cosmo Router execution config from subgraphs
+func GenerateCosmoRouterConfig(subGraphs []*model.SubGraph) (string, error) {
+	// Build the Cosmo router config structure
+	// This is a simplified version - you may need to adjust based on actual Cosmo requirements
+	config := map[string]interface{}{
+		"version":   "1",
+		"subgraphs": convertSubGraphsToCosmo(subGraphs),
+		// Add other Cosmo-specific configuration as needed
+	}
+
+	// Marshal to JSON
+	configJSON, err := json.MarshalIndent(config, "", "  ")
+	if err != nil {
+		return "", fmt.Errorf("marshal cosmo config: %w", err)
+	}
+
+	return string(configJSON), nil
+}
+
+func convertSubGraphsToCosmo(subGraphs []*model.SubGraph) []map[string]interface{} {
+	cosmoSubgraphs := make([]map[string]interface{}, 0, len(subGraphs))
+
+	for _, sg := range subGraphs {
+		cosmoSg := map[string]interface{}{
+			"name": sg.Service,
+			"sdl":  sg.Sdl,
+		}
+
+		if sg.URL != nil {
+			cosmoSg["routing_url"] = *sg.URL
+		}
+
+		if sg.WsURL != nil {
+			cosmoSg["subscription"] = map[string]interface{}{
+				"url":                   *sg.WsURL,
+				"protocol":              "ws",
+				"websocket_subprotocol": "graphql-ws",
+			}
+		}
+
+		cosmoSubgraphs = append(cosmoSubgraphs, cosmoSg)
+	}
+
+	return cosmoSubgraphs
+}