Ability for helidon server to handle ProxyProtocol

[andimullaraj]

The Helidon server seems to provide support for assessing the type of connection based on incoming bytes. Based on that, it looks like the developers can potentially implement a ProxyProtocol handler which will consume in plain connection the first proxy-protocol bytes, then upgrade the connection to SSL. I am suggesting this implementation/handler be available in Helidon server.

In particular:

• I am not suggesting that the Helidon server infer if proxy-protocol bytes are received and optionally consume them. Instead, the setting is static for a certain server-port and the bytes should always be there.
• Support for proxy-protocol v1 and v2
• The fetched values should be made available via the connection properties

[barchetta]

See also #7458

[trentjeff]

See also https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt

[spericas]

@andimullaraj Implementation is under review here #7829