Splitting pkgmgr and portmgr

Hello everyone,

It's been a while since the ports management team (portmgr) needed some
modernization and updates. To meet today's requirements, we are taking a first
step: spliting portmgr and pkgmgr.

While portmgr's charter does not change, the part of the responsibility
regarding the packages management will now be delegated to pkgmgr under the
portmgr umbrella.

Package management (pkgmgr) team:
  - its role is to work on the technical side of the package production:
      + building official packages.
      + running exp-runs.
      + maintaining and upgrading the package build infrastructure.
  - This team will be composed of people that are not part of the portmgr team
    (no votes for instance) but still will receive the portmgr emails (like
    lurkers) in a advisory function. Working on the package build
    infrastructure side they may have insights on subjects that are not clear
    to most portmgr members.

pkgmgr charter is:
  - Make sure the ports tree remains functional, this includes running test
    builds of proposed changes and reverting/fixing broken commits that break
    the build.
  - Maintain the automated package building cluster, and provide the resulting
    packages for download by FreeBSD users.

As such, bdrewery@ and antoine@ have stepped down from portmgr and joined
pkgmgr.

This change allows portmgr to focus on other areas of its charters, such as
communicate more with the community, help and advise any member of the ports
community to work on framework related changes, etc.

More changes may happen in the near future when this change has landed.

We would like to take the opportunity of this email to thank both antoine and
bdrewery for the work and the time spent on portmgr, and whish them luck in
their new role as pkgmgr.

Best regards,
Bapt on behalf of portmgr