feat: MIN constant as a source option (#3639)

* feature request #1635

- added MIN (-MAX -> -1024) as source

* fix rebase

* fix rebase

* change to use language strings for MIN/MAX instead of instance

updated CN and TX language file for MINuse -RESX for MIN instead of magi numbercode cleanup

* updated test sources

* updated JP language

* JP language: changed translation text

* updated HE language translations

radio/src/mixer.cpp

@@ -361,6 +361,9 @@ getvalue_t getValue(mixsrc_t i, bool* valid)
   }
 #endif
 
+  else if (i == MIXSRC_MIN) {
+    return -RESX;
+  }
   else if (i == MIXSRC_MAX) {
     return RESX;
   }