The [WebSockets spec](https://www.rfc-editor.org/rfc/rfc6455) states
that text messages must be valid UTF-8 encoded strings, which protobuf
messages virtually never are. This now correctly sends the protobuf events
as binary messages.
We change the format to correspond to CloudEvents, as originally intended,
and remove a redundant timestamp and newline.
We also bump the eventlogger to fix a race condition that this code triggers.
Creates a new `eventbus` package under `vault` with
an implementation of the `go-eventlogger` broker.
Also creates a stub of a common broker that will be accessible
in the core, and creates a simple event sending interface.
