Feature test for wp network option suggestion

[shawnhooper]

Relates to #322

This PR adds a feature test for suggesting wp network meta if the user types wp network option.

NOTE: This PR will fail until wp-cli/wp-cli#5879 is merged. This suggestion is changed in the wp-cli repo - but the command to test it is in the entity-command repo.

[danielbachhuber]

@shawnhooper Let's add this feature test to wp-cli/wp-cli#5879.

wp-cli/wp-cli requires wp-cli/entity-command as a dependency, so there shouldn't be any problem including it.