cms demos: print signingTime attributes

cms demos: print signingTime attributes

Add a makefile for the cms demos, and add a routine to cms_ver.c to
print any signingTime attributes from the CMS_ContentInfo object.
This provides an example that could be extended if an application
wants to examine the purported signing times.

Part of #8026

Testing:

  $ cd demos/cms
  $ make test

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22618)