Various Arduino Board Links

Copy into: "File" > "Preferences" > "Additional boards manager URLs"
RPi Pico/Pico2 type boards: https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
ESP8266 type boards: https://arduino.esp8266.com/stable/package_esp8266com_index.json
ESP32 type boards: https://espressif.github.io/arduino-esp32/package_esp32_index.json