RPM: Split out pam_zfs_key into separate package

Create a separate pam_zfs_key package for the PAM module components,
an optional addition to the deliverables, in much the same way as the
Python bindings are released as a separate python#-pyzfs package.

This makes it clear when the PAM module is shipped with the package,
since it's now in its own package.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Chris Lindee <chris.lindee+github@gmail.com>
Closes: #13026