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.
Also updates the event receieved to include a timestamp.
Websockets support both JSON and protobuf binary formats.
This can be used by either `wscat` or the new
`vault events subscribe`:
e.g.,
```sh
$ wscat -H "X-Vault-Token: $(vault print token)" --connect ws://127.0.0.1:8200/v1/sys/events/subscribe/abc?json=true
{"event":{"id":"5c5c8c83-bf43-7da5-fe88-fc3cac814b2e", "note":"testing"}, "eventType":"abc", "timestamp":"2023-02-07T18:40:50.598408Z"}
...
```
and
```sh
$ vault events subscribe abc
{"event":{"id":"5c5c8c83-bf43-7da5-fe88-fc3cac814b2e", "note":"testing"}, "eventType":"abc", "timestamp":"2023-02-07T18:40:50.598408Z"}
...
```
Co-authored-by: Tom Proctor <tomhjp@users.noreply.github.com>
