* Add support for PROXY protocol v2 in TCP listener

I did not find tests for this so I added one trying to cover different
configurations to make sure I did not break something. As far as I know,
the behavior should be exactly the same as before except for one thing
when proxy_protocol_behavior is set to "deny_unauthorized", unauthorized
requests were previously silently reject because of https://github.com/armon/go-proxyproto/blob/7e956b284f0a/protocol.go#L81-L84
but it will now be logged.

Also fixes https://github.com/hashicorp/vault/issues/9462 by adding
support for `PROXY UNKNOWN` for PROXY protocol v1.

Closes https://github.com/hashicorp/vault/issues/3807



* Add changelog
Co-authored-by: Rémi Lapeyre <remi.lapeyre@lenstra.fr>