Feature/ab#1767 make positionsource read nmea sentences from command

[flonix8]

Description

This pull request adds support for reading GPS data from an external command.

New feature: Command-based GPS reader

• Introduced CommandGpsReader in commandreader.py to read GPS data from the stdout of an arbitrary command, running in a separate thread and parsing NMEA sentences for position updates.
• Added GPSCommandConfig to the configuration, allowing users to specify a command as a list of strings to be executed for GPS data input.
• Updated the documentation (README.md) and the settings.template.yaml to explain and provide examples for using the command-based GPS reader.

Refactoring and type improvements

• Refactored the serial GPS reader: renamed GpsReader to SerialGpsReader, renamed GpsDeviceError to SerialGpsError, and moved the GpsPosition type to a new datatypes.py module for shared use.
• Updated the configuration (config.py) to use explicit types for each GPS source (GPSStaticConfig, GPSSerialConfig, GPSCommandConfig), improving clarity and extensibility.

Motivation and Context

How has this been tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.