doc: run rst2* with --strict to catch warnings

doc: run rst2* with --strict to catch warnings

Basically -Werror for docutils.

Fix all issues raised by this. The following issue
classes were reported:

Possible title underline, too short for the title.
Treating it as ordinary text because it's so short.
(:: at the start of the line directly below text,
either add empty line of merge into : on previous line)

Enumerated list start value not ordinal-1
(error in numbering)

Change-Id: Id3b0f7be4602f70115c60e6ddb89f6ed58e94e64
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20230331132429.601635-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26567.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit fafb05f6f3a7a1b46c278961ec8d2d8970f01096)