Add plugins command

[DavidWells]

Add ability for users to install additional commands

# list installed plugins
netlify plugins
# install plugin
netlify plugins:install netlify-name-of-thing-plugin
# remove plugin
netlify plugins:uninstall netlify-name-of-thing-plugin
# updates installed plugins to latest versions
netlify plugins:update

Plugins should follow a naming convention like: netlify-name-of-thing-plugin.

(netlify-{name-of-thing}-plugin)

Future:

# Search plugin repo for available plugins 
netlify plugins:search query

• Add commands
• document how to create plugins

[swyxio]

ideally also document how plugins are different from addons (different access levels etc)

[bcomnes]

Oh yeah, good point. Might be a point of confusion.