uniq-by command (#7295)

New command `uniq-by` to get uniq results by column.

Closes https://github.com/nushell/nushell/issues/7109

crates/nu-command/tests/commands/mod.rs

@@ -88,6 +88,7 @@ mod touch;
 mod transpose;
 mod try_;
 mod uniq;
+mod uniq_by;
 mod update;
 mod upsert;
 mod url;