Add jump to date functionality to date headers in timeline v2 (#7339)

Fix https://github.com/vector-im/element-web/issues/7677

Utilizes MSC3030: https://github.com/matrix-org/matrix-doc/pull/3030

https://user-images.githubusercontent.com/558581/150060664-79627573-f4fd-497c-b726-dc3485854bd0.png

src/settings/Settings.tsx

@@ -358,7 +358,7 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         // by default. We will conditionally show it depending on whether we can
         // detect MSC3030 support (see LabUserSettingsTab.tsx).
         // labsGroup: LabGroup.Messaging,
-        displayName: _td("Jump to date (adds /jumptodate)"),
+        displayName: _td("Jump to date (adds /jumptodate and jump to date headers)"),
         supportedLevels: LEVELS_FEATURE,
         default: false,
     },