Allow Undertow's server and socket options to be configured via the environment

[wilkinsona]

Something like:

server.undertow.options.socket.whatever: foo
server.undertow.options.server.whatever: bar

whatever is then coerced into one of the constants on UndertowOptions, ideally with relaxed binding. A concrete example:

server.undertow.options.server.enable-http2: true

See #3350 which this issue probably supersedes.

[snicoll]

Enum has already some kind of relaxed bindings and you'll need to make a Map<UndertowOptions, Object> to make that work. I believe the jackson support has something of the kind for includes.

[wilkinsona]

If only UndertowOptions were an Enum

[mbhave]

Closing in favor of PR #17356.