Problem Description: need to get eda content displaying as part of galaxy api and UI

Proposed Solution:

• Look for extension plugins listed in meta/extensions.yml
• Add support for 2 extensions: `eda/plugins/event_filters` and `eda/plugins/event_sources` (not adding support for custom extensions)
• Keep our collection content naming convention, where galaxy uses the same names as core (keeps naming standard and unambiguous)… ansible-doc takes names such as `module` `connection` `inventory`, and for extensions it will be `eda/plugins/event_filters` and `eda/plugins/event_sources`.
• Add the extensions to the contents list so it can be picked up by the galaxy api and UI