mgr/prometheus: use vendored "packaging" instead

mgr/prometheus: use vendored "packaging" instead

instead of using the top-level "packaging" module, use the one
vendored by setuptools.

packaging python module provides versioning defined by PEP-440.
but python3-packaging is provided by CentOS8 powertools repo,
which is not enabled by default. and in CentOS9, this package
is provided by AppStream instead of BaseOS.

as prometheus mgr module is included by ceph-mgr-module-core,
it would be desirable if our user can install ceph-mgr-module-core
without enabling powertools or AppStream repo on a CentOS or
its derivative distros.

fortunately, setuptools vendors packaging module. and both
CentOS8 and CentOS9 provide python3-setuptools in their BaseOS
repos.

in this change, instead of using "packging" module, we use the
venderored one, which is in turn embedded in pkg_resources.
this python module is provided by python3-setuptools on CentOS
distros, and python3-pkg-resources on Debian and its derivatives.

the packaging recipes are updated accordingly to reflect the
new runtime dependency.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>