✨ FLY Mini for stm32duino (#22356)

Marlin/src/pins/pins.h

 #elif MB(TRIGORILLA_PRO)
   #include "stm32f1/pins_TRIGORILLA_PRO.h"      // STM32F1                                env:trigorilla_pro
 #elif MB(FLY_MINI)
-  #include "stm32f1/pins_FLY_MINI.h"            // STM32F1                                env:FLY_MINI
+  #include "stm32f1/pins_FLY_MINI.h"            // STM32F1                                env:FLY_MINI env:FLY_MINI_maple
 #elif MB(FLSUN_HISPEED)
   #include "stm32f1/pins_FLSUN_HISPEED.h"       // STM32F1                                env:flsun_hispeedv1
 #elif MB(BEAST)

ini/stm32f1.ini

 build_flags = ${common_stm32.build_flags}
   -DHAL_PCD_MODULE_ENABLED -DDISABLE_GENERIC_SERIALUSB -DHAL_UART_MODULE_ENABLED
 src_filter  = ${common.default_src_filter} +<src/HAL/STM32>
+
+#
+# FLY Mini (STM32F103RCT6)
+#
+[env:FLY_MINI]
+platform             = ${common_stm32.platform}
+extends              = common_stm32
+build_flags          = ${common_stm32.build_flags} -DSS_TIMER=4
+board                = genericSTM32F103RC
+board_build.core     = stm32
+board_build.variant  = MARLIN_F103Rx
+board_build.offset   = 0x5000
+board_upload.offset_address  = 0x08005000
+extra_scripts        = ${common_stm32.extra_scripts}
+  pre:buildroot/share/PlatformIO/scripts/generic_create_variant.py
+  buildroot/share/PlatformIO/scripts/stm32_bootloader.py