Is your feature request related to a problem? Please describe.
Salt extensions are a good way of developing and distributing custom functionality for Salt. In particular, they are a superior alternative to custom modules when they are more complicated than a few lines. Salt-SSH syncs custom modules to the target, but extensions are disregarded.

This is more critical for 3008.0, which will remove many inbuilt modules in favor of Salt extensions.

Describe the solution you'd like
Salt-SSH should automatically discover installed packages that provide salt.loader entrypoints and include them in the generated thin archive.

Describe alternatives you've considered
Use custom modules instead.