add coreutils to cp search terms (#10738)

# Description

This PR is just a quick change to add `coreutils` to the `cp` command. I
thought that it would be a good search term as we start to integrate
more `coreutils` commands.

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crates/nu-command/src/filesystem/ucp.rs

@@ -35,7 +35,7 @@ impl Command for UCp {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["copy", "file", "files"]
+        vec!["copy", "file", "files", "coreutils"]
     }
 
     fn signature(&self) -> Signature {