feat: Support all current timezones for GPS (#3406)

* Support all current timezones.

* Fix function name and calculation for timezone offset.

* Allow setting any time offset value from -12 to +14 in 15 minutes increments.

* Alternate timezone editor in Companion (from elecpower).

* Fix compiler warning.

* chore: Add the T20

radio/src/storage/yaml/yaml_datastructs_tpro.cpp

@@ -263,7 +263,8 @@ static const struct YamlNode struct_CustomFunctionData[] = {
 };
 static const struct YamlNode struct_RadioData[] = {
   YAML_UNSIGNED( "manuallyEdited", 1 ),
-  YAML_PADDING( 7 ),
+  YAML_SIGNED( "timezoneMinutes", 3 ),
+  YAML_PADDING( 4 ),
   YAML_CUSTOM("semver",nullptr,w_semver),
   YAML_CUSTOM("board",nullptr,w_board),
   YAML_ARRAY("calib", 48, 12, struct_CalibData, NULL),