lvmconfig: add --type full to display full tree of settings

lvmconfig: add --type full to display full tree of settings

The lvmconfig --type full is actually a combination of --type current
and --type missing together with --mergedconfig options used.

The overall outcome is a configuration tree with settings as LVM sees
it when it looks for the values - that means, if the setting is defined
in some config source (lvm.conf, --config, lvmlocal.conf or any profile
that is used), the setting is used. Otherwise, if the setting is not
defined in any part of the config cascade, the defaults are used.

The --type full displays exactly this final tree with all the values
defined, either coming from configuration tree or from defaults.