Replace Col(..., as_path=True) with Path combinable

[WaVEV]

No description provided.

[timgraham]

Emanuel and I discussed this over DM and decided the as_path is more explicit and clear than the _as_path attribute.

His comment about why this is necessary in the first place: "The main issue is: Mongo handles the lhs items in a different way that the rhs, but in Atlas it handles the rhs column as lhs. So that inconsistency makes as_path=True (or some other way to remove or add the $) necessary.