common/options,doc: extract formatted desc into .yaml.in

common/options,doc: extract formatted desc into .yaml.in

* add a field named "fmt_desc", which is the description formatted using
  reStructuredText. it is preserved as it is if it's different from the
  desc or long_desc of an option. we can consolidate it with long_desc
  in future, and use pretty printer which has minimal support for
  reStructuredText for printing the formatted descriptions for a better
  user experience of command line. but at this moment, fmt_desc has
  only one consumer: the "ceph_confval" sphinx extension which extracts
  and translate the options yaml file to reStructuredText, which is in
  turn rendered by sphinx.
* remove unused options from the doc
  - journal_queue_max_ops
  - journal_queue_max_bytes

Signed-off-by: Kefu Chai <kchai@redhat.com>