Add XIAO Wio-SX1262 overlay; support SX12xx bandwidths (including 62.5 kHz) as default

- boards/seeed/xiao_wio_sx1262: add overlay, .conf, board.yml
- app: support full set of SX12xx bandwidths; default BW set to 62 (62.5 kHz)
- Update Kconfig and prj.conf
- Update lora_modem.h/c for validation and mapping

boards/heltec/heltec_wifi_lora32_v3/board.yml

@@ -2,7 +2,6 @@ board:
   name: heltec_wifi_lora32_v3
   full_name: "Heltec WiFi LoRa 32 V3"
   vendor: heltec
-  url: https://heltec.org/project/wifi-lora-32-v3/
   socs:
     - name: esp32s3
       variants: