Gps fix type LED flash

#### Issue details
_Please describe the problem, or desired feature_
Currently we have a green flashing LED that indicates a 3DFix, a faster flash indicates dgps, but now we have RTK Float and RTK Fix, it would be nice to have an indication that these modes are active.

My personal preference is for the green to stay with a purple flash for 50ms every 1Hz for RTK float, and a double flash for RTK Fix.

#### Platform
[X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover

#### Airframe type
_What type of airframe (flying wing, glider, hex, Y6, octa etc)_

#### Hardware type
_What autopilot hardware was used? (pixhawk, pixracer, PX4FMU etc)_

#### Logs
_Please provide a link to any relevant logs that show the issue_

No file or test is named. Start by locating the existing green LED indications for 3D fix and DGPS across the all-platform autopilot code, then trace how RTK Float and RTK Fix states are exposed. Done means the requested purple flash patterns distinguish RTK Float from RTK Fix without breaking the existing indications.

Written by the indexing model from the issue text.