(#10940) Deprecate --apply in favor of --catalog

Without this patch, the puppet apply command uses the --apply option
to reference a Puppet catalog. This can cause a bit of confusion as both
the subcommand and option have the same name.

This patch improves the usability of the puppet apply command by
adding a new --catalog option. This patch also adds a deprecation
warning whenever the --apply option is used, which advises end-users
to use the --catalog option instead.

This patch updates the in-line help documentation by adding help output
for the new --catalog option, and adding a deprecation warning for the
--apply option.

The plan is to deprecate the --apply option in the next 2.7.x release,
and removal in the future. External documentation should be updated to
reflect the new preference towards using the --catalog option in-place
of --apply.

Preferred method of applying a Puppet catalog using puppet apply:

$ puppet apply --catalog <catalog>

This patch also includes the spec tests covering the changes in
behavior.