Add a meta/extensions.yml file for displaying EDA content in Automation Hub

[alisonlhart]

To display EDA content on Ansible Automation Hub, there is an additional file needed in the collection.

Add the meta/extensions.yml file to the collection with the following contents:

extensions:
  - args:
      ext_dir: eda/plugins/event_filter
  - args:
      ext_dir: eda/plugins/event_source

This will cause the EDA plugin to display under the collection's "Contents" tab in Automation Hub.

See the ansible.eda collection source for reference.

(Note: Depends on #67 to work properly)

[szh]

@cyberark-bizdev @infamousjoeg