Add cat and get-content to open's search terms (#15643)

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A friend of mine started using nushell on Windows and wondered why the
`cat` command wasn't available. I answered to him, that he can use `help
-f` or F1 to find the command but then we both realized that neither
`cat` nor `Get-Command` were part of `open`'s search terms. So I added
them.

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

@@ -34,7 +34,14 @@ impl Command for Open {
     }
 
     fn search_terms(&self) -> Vec<&str> {
-        vec!["load", "read", "load_file", "read_file"]
+        vec![
+            "load",
+            "read",
+            "load_file",
+            "read_file",
+            "cat",
+            "get-content",
+        ]
     }
 
     fn signature(&self) -> nu_protocol::Signature {