Doxygen2man (#388)

• doxygen2man: Add utility to generate man pages from doxygen

This is in here from kronosnet so it cna be used by other parts
of the cluster stack.

• [man] drop trailing white spaces

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

• [build] cleanup variable names

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

• [build] add conditionals to use internal or external doxygen2man

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

• Update .gitignore

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

Co-authored-by: Christine Caulfield <ccaulfie@redhat.com>