Add option to display the OSD logo on arming

Adds `osd_logo_on_arming` setting with values `OFF, ON, FIRST_ARMING` (defaults to `OFF`). Optionally displays the OSD splash logo durin the "ARMING" message.

src/main/osd/osd.h

@@ -271,6 +271,7 @@ typedef struct osdConfig_s {
     int8_t rcChannels[OSD_RCCHANNELS_COUNT];  // RC channel values to display, -1 if none
     uint8_t displayPortDevice;                // osdDisplayPortDevice_e
     uint16_t distance_alarm;
+    uint8_t logo_on_arming;                   // show the logo on arming
 } osdConfig_t;
 
 PG_DECLARE(osdConfig_t, osdConfig);