ssh: Refine the modal UI (#19256)

This PR refines the SSH modal UI, adjusting spacing and alignment. Via
these changes, I'm also introducing the ability for the `empty_message`
on the `List` component to receive not just a string but any element.
The custom way in which the SSH modal was designed made it feel like
this was needed for proper spacing.

<img width="700" alt="Screenshot 2024-10-16 at 1 20 54 AM"
src="https://github.com/user-attachments/assets/f2e0586b-4c9f-4497-b4cb-e90c8157512b">


Release Notes:

- N/A

crates/ui/src/components/modal.rs

@@ -77,6 +77,7 @@ impl RenderOnce for Modal {
                 v_flex()
                     .id(self.container_id.clone())
                     .w_full()
+                    .flex_1()
                     .gap(Spacing::Large.rems(cx))
                     .when_some(
                         self.container_scroll_handler,
@@ -344,6 +345,7 @@ impl RenderOnce for Section {
         } else {
             v_flex()
                 .w_full()
+                .flex_1()
                 .gap_y(Spacing::Small.rems(cx))
                 .when(self.padded, |this| {
                     this.px(Spacing::Medium.rems(cx) + Spacing::Medium.rems(cx))