Add channels panel with stubbed out information

co-authored-by: nate <nate@zed.dev>

crates/gpui/src/elements/flex.rs

@@ -22,6 +22,7 @@ pub struct Flex<V: View> {
     children: Vec<AnyElement<V>>,
     scroll_state: Option<(ElementStateHandle<Rc<ScrollState>>, usize)>,
     child_alignment: f32,
+    spacing: f32,
 }
 
 impl<V: View> Flex<V> {
@@ -31,6 +32,7 @@ impl<V: View> Flex<V> {
             children: Default::default(),
             scroll_state: None,
             child_alignment: -1.,
+            spacing: 0.,
         }
     }
 
@@ -42,6 +44,11 @@ impl<V: View> Flex<V> {
         Self::new(Axis::Vertical)
     }
 
+    pub fn with_spacing(mut self, spacing: f32) -> Self {
+        self.spacing = spacing;
+        self
+    }
+
     /// Render children centered relative to the cross-axis of the parent flex.
     ///
     /// If this is a flex row, children will be centered vertically. If this is a