Support Helm `local` protocol

[Schille]

At this location

getdeck/getdeck/sources/file.py

Line 43 in 6673a83

handler = methodcaller(f"fetch_{self.type}", **kwargs)

Helm fetcher does not support type == "local" as it is currently not implemented.

[tobifroe]

This would be super helpful for a dev setup I'm working on.