The build fails with warnings when the ".. only:: opensource" directive includes links

[annastuchlik]

In the docs/architecture/raft.rst file, there is an .. only:: opensource directive that includes a link.

.. note::
  In ScyllaDB 5.2 and ScyllaDB Enterprise 2023.1 Raft is Generally Available and can be safely used for consistent schema management.
  It will get enabled by default when you upgrade your cluster to ScyllaDB 5.4 or 2024.1.
  If needed, you can explicitly prevent it from getting enabled upon upgrade.

  .. only:: opensource

    See :doc:`the upgrade guide from 5.2 to 5.4 </upgrade/upgrade-opensource/upgrade-guide-from-5.2-to-5.4/upgrade-guide-from-5.2-to-5.4-generic>` for details.

The section wrapped in the .. only:: opensource directive is correctly excluded from the Enterprise documentation, but the Enterprise builds are failing with a warning about that link, for example: https://github.com/scylladb/scylla-enterprise/pull/3242:
/home/runner/work/scylla-enterprise/scylla-enterprise/docs/architecture/raft.rst:45: WARNING: unknown document: '/upgrade/upgrade-opensource/upgrade-guide-from-5.2-to-5.4/upgrade-guide-from-5.2-to-5.4-generic'

I'll remove that link so that the Enterprise builds don't fail, but we should find a way to exclude links in a way that won't trigger warnings.