man/help: change LV type listing

man/help: change LV type listing

Previously, accepted LV types were presented as a series of suffixes
after the "LV" on the command line.  The addition of many new types
resulted in this becoming too long, e.g

  lvconvert --type cache --cachepool LV LV_linear_striped_thinpool_vdo_vdopool_vdopooldata_raid

For man pages, move these types from the command line to a new line
dedicated to listing accepted LV types:

  lvconvert --type cache --cachepool LV LV1
  ...

  LV1 types: linear striped thinpool vdo vdopool vdopooldata raid

The special "LV1" is used as a reference to avoid confusion
with other LVs that may appear on the command line.  There
are currently no commands with more than one typed LV, but
if there are cases with more, then "LV2" could also be used.

For command line usage/-h output, drop the LV types from the
command line specification.  The more detailed is not needed
in the help output and can be found in the man page.