VAULT-17772: bump go-eventlogger to v0.2.1

[peteski22]

This PR updates the version of go-eventlogger to v0.2.1, which provides the ability to remove nodes when removing a pipeline, previously we didn't remove nodes and risked slowly leaking memory as web-sockets subscribed => unsubscribed from the eventbus.

Some logic has been added to handle logging depending on whether:

1. Pipeline was removed but there was an error removing the referenced nodes.
2. Pipeline was not removed (and therefore referenced nodes remain too).

Small other changes:

• NewBroker returns an error param
• Close now requires context

The bump to v0.2.1 is required as we move audit to use eventlogger too and will need to clear up nodes and pipelines.

[swenson]

LGTM

Thanks for this work in go-eventlogger!