add ItsyBitsy nRF52840 to board list

Author: hathach

bpt.ini

@@ -261,6 +261,9 @@ index_template =
         }},
         {{
            "name":"Adafruit Metro nRF52840 Express"
+        }},
+        {{
+           "name":"Adafruit ItsyBitsy nRF52840"
         }}
      ],
      "toolsDependencies": [

package_adafruit_index.json

@@ -4162,6 +4162,9 @@
             },
             {
               "name": "Adafruit Metro nRF52840 Express"
+            },
+            {
+              "name": "Adafruit ItsyBitsy nRF52840"
             }
           ],
           "toolsDependencies": [
@@ -4328,4 +4331,4 @@
       ]
     }
   ]
-}
+}