add input_output type to input list to return string (#9557)

# Description

This PR fixes a bug that @amtoine found. It adds an input_output type so
that `input list`'s signature supports `string` as an output.

## Before

![image](https://github.com/nushell/nushell/assets/343840/7ee2b672-9976-4c69-a9a2-686ddbd3a60d)
```
Signatures:
  list<any> | input list <string?> -> list<any>
```

## After

![image](https://github.com/nushell/nushell/assets/343840/f86747cf-a134-4bb0-b89c-2e28f590f3c3)
```
Signatures:
  list<any> | input list <string?> -> list<any>
  list<string> | input list <string?> -> <string>
```

# User-Facing Changes
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crates/nu-command/src/platform/input/list.rs

@@ -39,10 +39,13 @@ impl Command for InputList {
 
     fn signature(&self) -> Signature {
         Signature::build("input list")
-            .input_output_types(vec![(
-                Type::List(Box::new(Type::Any)),
-                Type::List(Box::new(Type::Any)),
-            )])
+            .input_output_types(vec![
+                (
+                    Type::List(Box::new(Type::Any)),
+                    Type::List(Box::new(Type::Any)),
+                ),
+                (Type::List(Box::new(Type::String)), Type::String),
+            ])
             .optional("prompt", SyntaxShape::String, "the prompt to display")
             .switch(
                 "multi",