"short" Welcome Banner option (#14638)

# Description

Adds:

```nushell
$env.config.show_banner = "short"
```

This will display *only* the startup time. That was the only information
from the banner that the user couldn't possibly include in their own
config/banner (since it is `-1ns` during startup). This allows one to
create their own banner and yet still show the startup time.

Example (can be a file named `banner.nu` in autoloads:

```nushell
$env.config.show_banner = "short"

let ver = (version)
print $"(ansi blue_bold)Nushell Release:(ansi reset) ($ver.version) \(($ver.build_os)\)"
```


![image](https://github.com/user-attachments/assets/dd9d53a2-d89a-432e-8fa3-2d65072e08b1)


---

`true` and `false` settings continue to work as they do today. `true` is
still the default.

# User-Facing Changes

New configuration option:

```nushell
$env.config.show_banner = "short"
```

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

◼️ Update doc
◼️ Update `doc_config.nu`

crates/nu-cli/src/repl.rs

@@ -146,15 +146,30 @@ pub fn evaluate_repl(
     // Regenerate the $nu constant to contain the startup time and any other potential updates
     engine_state.generate_nu_constant();
 
-    if load_std_lib.is_none() && engine_state.get_config().show_banner {
-        eval_source(
-            engine_state,
-            &mut unique_stack,
-            r#"banner"#.as_bytes(),
-            "show_banner",
-            PipelineData::empty(),
-            false,
-        );
+    if load_std_lib.is_none() {
+        match engine_state.get_config().show_banner {
+            Value::Bool { val: false, .. } => {}
+            Value::String { ref val, .. } if val == "short" => {
+                eval_source(
+                    engine_state,
+                    &mut unique_stack,
+                    r#"banner --short"#.as_bytes(),
+                    "show short banner",
+                    PipelineData::empty(),
+                    false,
+                );
+            }
+            _ => {
+                eval_source(
+                    engine_state,
+                    &mut unique_stack,
+                    r#"banner"#.as_bytes(),
+                    "show_banner",
+                    PipelineData::empty(),
+                    false,
+                );
+            }
+        }
     }
 
     kitty_protocol_healthcheck(engine_state);