Path commands: Put column path args behid flag; Allow path join appending without flag (#4008)

* Change path join signature

* Appending now works without flag
* Column path operation is behind a -c flag

* Move column path arg retrieval to a function

Also improves errors

* Fix path join tests

* Propagate column path changes to all path commands

* Update path command examples with columns paths

* Modernize path command examples by removing "echo"

* Improve structured path error message

* Fix typo

crates/nu-engine/src/from_value.rs

@@ -101,6 +101,7 @@ impl FromValue for i64 {
         v.as_i64()
     }
 }
+
 impl FromValue for Tagged<i64> {
     fn from_value(v: &Value) -> Result<Self, ShellError> {
         let tag = v.tag.clone();