add arguments to build-pkgs.sh: -d|-h|-r|-s|-u|-uo|-v

I'd like to enrich the experience of ./build-pkgs.sh by:

• adding these flags to it:

  [-d|--debug]                              enable debug mode, showing every executed command
  [-h|--help]                               print usage (this text)
  [-u|--upload ${WHERE}]                    upload packages to: nexus, cloudsmith, both?
  [-uo|--upload-only ${WHERE}]              skip build and upload packages that are already built to: nexus, cloudsmith, both

• migrating these parameters from positional to double-dash notation:

  [-r|--reuse-pkg-version ${PKG_VERSION}]   version of package to reuse e.g. isc20220801123456
  [-s|--systems ${SYSTEMS}]                 list of distros e.g. "debian-11 fedora-36"
  [-v|--version ${KEA_VERSION}]             Kea version in format ${major}.${minor} e.g. 2.3