LP1940146: Debian Bullseye Installation Support

LP1940146: Debian Bullseye Installation Support

Update documentation and prerequisite installation Makefiles to add
support for Debian Bullseye (11.0).

Use PKG_CHECK_MODULES instead of AC_CHECK_PROG to test for the
presence of yaz.  This is done because of the following Changelog
entry:

    yaz-config and its man page are no longer packaged.  Please switch
    to pkg-config (yaz, yaz-icu or yaz-server).  This also makes the
    package reproducible.  Closes: #955501

This change works on all currently supported Evergreen distros.  You
can test it by running autoreconf -f and then running the normal
configure command.

Signed-off-by: Jason Stephenson <jason@sigio.com>
Signed-off-by: Chris Sharp <csharp@georgialibraries.org>