Add ControlGroup

[carson-katri]

Closes #119

<text><%= @number %></text>
<control-group>
  <control-group:label>
    <label system-image="gear">Options</label>
  </control-group:label>
  <control-group:content>
    <%= for item <- 1..5 do %>
      <button phx-click="set_number" phx-value-number={item}>Item #<%= item %></button>
    <% end %>
  </control-group:content>
</control-group>

Simulator.Screen.Recording.-.iPhone.14.Pro.-.2023-02-09.at.10.45.52.mp4

This will become more useful once we have the toolbar modifier.

[carson-katri]

#172 should be merged first, so I can add tests.