`HEAD /bytes` does not seem to return Content Type as stated in API Docs

[Cafe137]

https://docs.ethswarm.org/api/#tag/Bytes/paths/~1bytes~1%7Breference%7D/head

Requests the headers containing the content type and length for the reference

The content type is always application/octet-stream. If it is irrecoverable (only available in the mantaray metadata), it should be removed from the docs.

Relevant code:

https://github.com/ethersphere/bee/blob/master/pkg/api/bytes.go#L214