feat(core): refactor sidebar header (#6251)

- Add user avatar
- Move sign-out/user settings link from workspace-modal to user avatar modal
- Modify the style of workspace list items
- Modify gap of navigation buttons
- Animate Syncing/Offline/...

![CleanShot 2024-03-22 at 10.22.38.gif](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/LakojjjzZNf6ogjOVwKE/7305f561-a85b-4ec6-89c2-27e2f1b63c85.gif)

packages/frontend/core/public/imgs/unknown-user.svg

@@ -0,0 +1,17 @@
+<svg width="20" height="20" viewBox="0 0 20 20" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <g clip-path="url(#clip0_19485_742)">
+    <rect width="20" height="20" rx="10" fill="currentColor" fill-opacity="0.1" />
+    <path
+      d="M10 10.9999C12.0829 10.9999 13.7714 9.29858 13.7714 7.1999C13.7714 5.10122 12.0829 3.3999 10 3.3999C7.91709 3.3999 6.22857 5.10122 6.22857 7.1999C6.22857 9.29858 7.91709 10.9999 10 10.9999Z"
+      fill="currentColor" fill-opacity="0.3" />
+    <path
+      d="M1.5 22.3999C1.33431 22.3999 1.19948 22.2649 1.20496 22.0993C1.36224 17.3416 5.23972 13.5332 10 13.5332C14.7603 13.5332 18.6378 17.3416 18.795 22.0993C18.8005 22.2649 18.6657 22.3999 18.5 22.3999H1.5Z"
+      fill="currentColor" fill-opacity="0.3" />
+  </g>
+  <defs>
+    <clipPath id="clip0_19485_742">
+      <rect width="20" height="20" rx="10" fill="white" />
+    </clipPath>
+  </defs>
+</svg>
+