Prior to this commit, all supported servers would share the same
configuration property `server.connection-timeout`. Unfortunately, in
many cases the behavior of this timeout changes depending on the server.
From actual connection setup timeout, to detecting and closing idle
connections, this property cannot be properly translated from one server
implementation to another.

This commit deprecates this configuration property and introduces server
specific properties:

* `server.jetty.connection-idle-timeout`
(Time that the connection can be idle before it is closed.)
* `server.netty.connection-timeout`
(Connection timeout of the Netty channel.)
* `server.tomcat.connection-timeout`
(Amount of time the connector will wait, after accepting a connection,
for the request URI line to be presented.)
* `server.undertow.no-request-timeout`
(Amount of time a connection can sit idle without processing a request,
before it is closed by the server.)

`server.connection-timeout` is now deprecated and will be removed in a
future release.

Fixes gh-18473