Categorification: move Path commands out of the default category (#9937)

Path commands were incorrectly located in the default category...

This PR moves all of the *Path* commands into their own Category called
*Path*

crates/nu-protocol/src/signature.rs

@@ -60,6 +60,7 @@ pub enum Category {
     Math,
     Misc,
     Network,
+    Path,
     Platform,
     Random,
     Shells,
@@ -91,6 +92,7 @@ impl std::fmt::Display for Category {
             Category::Math => "math",
             Category::Misc => "misc",
             Category::Network => "network",
+            Category::Path => "path",
             Category::Platform => "platform",
             Category::Random => "random",
             Category::Shells => "shells",