openhaystack: store battery status in FindMy packet

See also:
  seemoo-lab/openhaystack#185
  https://github.com/MatthewKuKanich/FindMyFlipper/blob/e5a678e33dd17af46bb63050be4c9d10e17f6252/FindMyFlipper/findmy_state.c#L126-L137

From biemster/FindMy#53
  Advertising byte:
    ?xx1rrmrr
    r: reserved
    m: maintained
    x: can be set. x must be:
      00: full
      01: medium
      10: low
      11: critical

  this doesn't seem to correspond with the above links

apps/openhaystack/ChangeLog

@@ -1,3 +1,4 @@
 0.01: New App!
 0.02: Keep advertising when connected
 0.03: Use ble_advert module to work with other BLE advert apps
+0.04: Update battery status in advertising packet

apps/openhaystack/custom.html

@@ -38,7 +38,12 @@
 {
 const key = E.toUint8Array(atob(${JSON.stringify(keyValue)})); // public key
 const mac = [ key[0] | 0b11000000, key[1], key[2], key[3], key[4], key[5] ].map(x => x.toString(16).padStart(2, '0')).join(':'); // mac address
-const adv = [ 0x1e, 0xff, 0x4c, 0x00, 0x12, 0x19, 0x00, key[6], key[7], key[8], key[9], key[10], key[11], key[12], key[13], key[14], key[15], key[16], key[17], key[18], key[19], key[20], key[21], key[22], key[23], key[24], key[25], key[26], key[27], key[0] >> 6, 0x00 ]; // advertising packet
+let batt = E.getBattery();
+if (batt > 80) batt = 0x0; // full
+else if (batt > 50) batt = 0x50; // medium
+else if (batt > 20) batt = 0xa0; // low
+else batt = 0xf0; // critical
+const adv = [ 0x1e, 0xff, 0x4c, 0x00, 0x12, 0x19, batt, key[6], key[7], key[8], key[9], key[10], key[11], key[12], key[13], key[14], key[15], key[16], key[17], key[18], key[19], key[20], key[21], key[22], key[23], key[24], key[25], key[26], key[27], key[0] >> 6, 0x00 ]; // advertising packet
 NRF.setAddress(mac);
 require("ble_advert").push(adv, {whenConnected: true, interval: 1000}); // advertise AirTag *and* normal device name (to remain connectable)
 }

apps/openhaystack/metadata.json

@@ -1,7 +1,7 @@
 { "id": "openhaystack",
   "name": "OpenHaystack (AirTag)",
   "icon": "icon.png",
-  "version":"0.03",
+  "version":"0.04",
   "description": "Copy a base64 key from https://github.com/seemoo-lab/openhaystack and make your Bangle.js trackable as if it's an AirTag",
   "tags": "openhaystack,bluetooth,ble,tracking,airtag",
   "type": "bootloader",