pio update - flash size of non-standard boards

* adding missing flash size flags that were lost between 0.14 and 0.15
   (necessary if you don't flash using esptool)
* adding env:esp32dev_16M for 16MB flash (serg74 esp32-16M, twilightlord esp32 16M)

platformio_override.sample.ini

@@ -359,6 +359,8 @@ upload_speed = 115200
 lib_deps = ${esp32c3.lib_deps}
 board_build.partitions = tools/WLED_ESP32_2MB_noOTA.csv
 board_build.flash_mode = dio
+board_upload.flash_size = 2MB
+board_upload.maximum_size = 2097152
 
 [env:wemos_shield_esp32]
 board = esp32dev