add c6 (experimental), upgrade AsyncWebServer

boards/seeed_xiao_esp32c6.json

@@ -0,0 +1,48 @@
+{
+  "build": {
+    "core": "esp32",
+    "extra_flags": [
+      "-DARDUINO_XIAO_ESP32C6",
+      "-DARDUINO_USB_MODE=1",
+      "-DARDUINO_USB_CDC_ON_BOOT=1"
+    ],
+    "f_cpu": "160000000L",
+    "f_flash": "80000000L",
+    "flash_mode": "qio",
+    "hwids": [
+      [
+        "0x2886",
+        "0x0046"
+      ],
+      [
+        "0x303a",
+        "0x1001"
+      ]
+    ],
+    "mcu": "esp32c6",
+    "variant": "XIAO_ESP32C6"
+  },
+  "connectivity": [
+    "wifi",
+    "bluetooth",
+    "zigbee",
+    "thread"
+  ],
+  "debug": {
+    "openocd_target": "esp32c6.cfg"
+  },
+  "frameworks": [
+    "arduino",
+    "espidf"
+  ],
+  "name": "Seeed Studio XIAO ESP32C6",
+  "upload": {
+    "flash_size": "4MB",
+    "maximum_ram_size": 327680,
+    "maximum_size": 4194304,
+    "require_upload_port": true,
+    "speed": 460800
+  },
+  "url": "https://wiki.seeedstudio.com/XIAO_ESP32C6_Getting_Started/",
+  "vendor": "Seeed Studio"
+}