Edge supports summarizer Permissions Policy only behind flag (#27208)

Edge Summarizer permission policy is also behind a flag

Author: ddbeck

http/headers/Permissions-Policy.json

@@ -1167,7 +1167,16 @@
               "chrome_android": {
                 "version_added": false
               },
-              "edge": "mirror",
+              "edge": {
+                "version_added": "138",
+                "flags": [
+                  {
+                    "type": "preference",
+                    "name": "#edge-llm-summarization-api-for-phi-mini",
+                    "value_to_set": "Enabled"
+                  }
+                ]
+              },
               "firefox": {
                 "version_added": false
               },