Add --recently-active option in plugin list command

[ernilambar]

Related: #232

PR continued from #383

wp plugin list --recently-active 

This will give the list of recently active plugins.

[swissspidy]

Can we re-add some of the docs changes from #383?

Also, what's the main change here that made the tests pass?

[ernilambar]

• Examples updated
• Given a WP install was used for multisite functionality testing.

[ernilambar]

@swissspidy Is it worth adding --recently-active in wp plugin activate or we are good with wp plugin activate $(wp plugin list --recently-active --field=name ?