Add chain metadata

[marcelovani]

We have a new functionality on chains: The chain discovery
It allows us to run any chain just like any other command, e.g. without the --file argument

Here is an example of metadata that make the chain discoverable
https://github.com/hechoendrupal/drupal-console-core/blob/master/config/dist/chain/site-new.yml#L4..L6

This issue is to add the missing metadata on the optional chains found in
https://github.com/hechoendrupal/drupal-console-core/tree/master/config/dist/chain/optional

When adding metadata, if a chain should be discovered when there is no Drupal site, we need to add the respective metadata seen in #240