docs(security): update info on use of OpenSSL 3.0

docs(security): update info on use of OpenSSL 3.0

OpenSSL 3.0 is a pre-requisite since v2.7 and can be installed
on the operating system by updating the previous version.
However, this may not be convenient for everyone, as some may
want to keep their previous versions of OpenSSL.

This update on the docs shows that there is an alternative to
install OpenSSL on the system by using a local build of
OpenSSL 3.0 and pointing both the build and run commands to
that build.

Signed-off-by: Juan Pablo Conde <juanpablo.conde@arm.com>
Change-Id: Ib9ad9ee5c333f7b04e2747ae02433aa66e6397f3