In this PR, the two new variants for `ErrorKind`, `FileNotFound`
and `DirectoryNotFound` with a nice `not_found_as` method for the
`ErrorKind` to easily specify the `NotFound` errors. I also updated some
places where I could of think of with these new variants and the message
for `NotFound` is no longer "Entity not found" but "Not found" to be
less strange.
closes#15142closes#15055