Rework file picker for SSH modal (#19020)

This PR changes the SSH modal design so its more keyboard
navigation-friendly and adds the server nickname feature.

Release Notes:

- N/A

---------

Co-authored-by: Danilo <danilo@zed.dev>
Co-authored-by: Danilo Leal <67129314+danilo-leal@users.noreply.github.com>

crates/gpui/src/shared_string.rs

@@ -1,5 +1,6 @@
 use derive_more::{Deref, DerefMut};
 
+use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use std::{borrow::Borrow, sync::Arc};
 use util::arc_cow::ArcCow;
@@ -16,6 +17,16 @@ impl SharedString {
     }
 }
 
+impl JsonSchema for SharedString {
+    fn schema_name() -> String {
+        String::schema_name()
+    }
+
+    fn json_schema(gen: &mut schemars::gen::SchemaGenerator) -> schemars::schema::Schema {
+        String::json_schema(gen)
+    }
+}
+
 impl Default for SharedString {
     fn default() -> Self {
         Self(ArcCow::Owned(Arc::default()))