packages: Replace libbz2 package with a bzip2 package

Currently libbz2 is in the libbz2 package, while bzip2 itself is in
-utilities, which is inconsistent. Move both the library and the
utility to a new -bzip2 package, and use LIB_PACKAGE to create a
separate -bzip2-lib package for runtime dependencies.

Add the bzip2 package to the minimal set, and since newsyslogd uses
bzip2 for logfile compression, add a dependency from there.

MFC after: 1 day
Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D52663