enhancement(http sink, codecs): Integrate `encoding::Encoder` with `http` sink (#11647)

* Integrate `encoding::Encoder` with `http` sink
* Fix benches
* Remove `deny_unknown_fields` which conflicts with `flatten`
* Fix NDJSON test not containing trailing newline
* Remove trailing newline in NDJSON to keep backwards-compatibility with `0.20.x`
* Remove unused `HttpEventMissingMessageError` internal event

Signed-off-by: Pablo Sichert <mail@pablosichert.com>