harmonize all plugins docs

original issue #1012
 
Add a configuration section that lists all options for each plugin.
List options in alphabetic order.
Mention the default value for each option.
Use same sentences to describe concepts common to different plugins eg 'auto' option, install description
For empty string defaults, we could be more descriptive—in this case, something like "all interfaces" or "0.0.0.0", which is colloquially equivalent.