The LXC task driver documentation is missing for many of the optional
task config fields, and for the recently added `gc` field on the
driver configuration.
* call out pluggable drivers in task drivers section and link/add info to plugin stanza
* fix hyphenation
* removing page and nav that tells users drivers are not pluggable
* show new syntax for configuring raw_exec plugin on client
* enabled option value for raw_exec is boolean
* add plugin options section and mark client options as soon to be deprecated
* fix typos
* add plugin options for rkt task drivers and place deprecation warning in client options
* add some plugin options with plugin configuration example + mark client options as soon to be deprecated
* modify deprecation warning
* replace colon with - for options
* add docker plugin options
* update links within docker task driver to point to plugin options
* fix typo and clarify config options for lxc task driver
* replace raw_exec plugin syntax example with docker example
* create external section
* restructure lxc docs and add backward incompatibility warning
* update lxc driver doc
* add redirect for lxc driver doc
* call out plugin options and mark client config options for drivers as deprecated
* add placeholder for lxc driver binary download
* update data_dir/plugins reference with plugin_dir reference
* Update website/source/docs/external/lxc.html.md
Co-Authored-By: Omar-Khawaja <Omar-Khawaja@users.noreply.github.com>
* corrections
* remove lxc from built-in drivers navigation
* reorganize doc structure and fix redirect
* add detail about 0.9 changes
* implement suggestions/fixes
* removed extraneous punctuation
* add official lxc driver link
