Add a test for loading certificate and key to ssl context

Add a test for loading certificate and key to ssl context

The test certificate used in test_ssl.c is updated to use 2048 bit
RSA and the matching key is added.

Tests include loading certificate and key as inlined pem as well as
from files. Note that loading the key also checks that it matches
the certificate, providing an indirect test that the latter was loaded
correctly.

Change-Id: Ic6f089896191145f68ce9a11023587d05dcec4d8
Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20240906103814.36839-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg29074.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>