The pipeline should return the current active plugins

[ph]

The pipeline should be able to answer the following questions.

• returns activated plugins in that specific pipeline
• returns activated plugins grouped per type
• returns activated plugins filtered by type (input, output, filter, codec)

Either by keeping an internal registry or asking the specific ast for that pipeline.

Ref #2611

[jordansissel]

This is labeled metrics, but is more about 'current state' and less about performance/behavior. Does this sound right?

[ph]

Agree its more about manageability, we don't have an api tag yet.

[suyograo]

Fixed in alpha2