Documentation: ext4: Convert includes into toctrees

Documentation: ext4: Convert includes into toctrees

ext4 docs are organized in three master docs (overview.rst, globals.rst,
and dynamic.rst), in which these include other docs via include::
directive. These docs sturcture is better served by toctrees instead.

Convert the master docs to use toctrees.

Fixes: 0bf1f51e34c4 ("ext4: Add atomic block write documentation")
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Acked-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250620105643.25141-3-bagasdotme@gmail.com