git-p4: add config git-p4.pathEncoding

git-p4: add config git-p4.pathEncoding

Perforce keeps the encoding of a path as given by the originating OS.
Git expects paths encoded as UTF-8. Add a config to tell git-p4 what
encoding Perforce had used for the paths. This encoding is used to
transcode the paths to UTF-8. As an example, Perforce on Windows often
uses “cp1252” to encode path names.

Signed-off-by: Lars Schneider <redacted>
Acked-by: Luke Diamand <redacted>
Signed-off-by: Lars Schneider <redacted>
Signed-off-by: Junio C Hamano <redacted>