Doc: Update timeline documentation

- Added a task topic for binding a timeline to a property.
- Added topic on adding multilpe timelines.
- Some changes to focus more on the task rather than function.
- Other minor updates.

Task-number: QDS-6879
Change-Id: Ibd99785d6a9ee70fc10b8e1395ef8aaf0e186ddc
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

doc/qtdesignstudio/src/components/qtquick-component-context-menu.qdocinc

@@ -60,7 +60,7 @@
         \li \l{Lists and Other Data Models}
     \row
         \li Timeline
-        \li \l{Creating Timelines}
+        \li \l{Creating a Timeline}
     \if defined(qtdesignstudio)
     \row
         \li Event List