doc: use latest label instead of version in docs

Instead of having a .99 version, use latest and link to the lates
documentation on the left side bar.

The version number has been confusing users where it was difficult to
determine if they were looking at the development tree or some released
version.

Fixes #24453

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

doc/_templates/zversions.html

@@ -2,7 +2,7 @@
   <div class="rst-versions" data-toggle="rst-versions" role="note" aria-label="versions">
     <span class="rst-current-version" data-toggle="rst-current-version">
       <span class="fa fa-book"> Zephyr Project</span>
-      v: {{ current_version }}
+      v: <a href="/latest/">latest</a>
       <span class="fa fa-caret-down"></span>
     </span>
     <div class="rst-other-versions">