Support 100-Continue in Undertow transport out-of-the-box

to keep the behavior same as it in jetty transport.

Deploy a simple CXF SOAP service
Configure SoapUI in preferences > HTTP Settings (Expect-Continue: true)
Call a SOAP operation

100-Continue is well supported in the jetty transport by default, however currently with undertow transport we need to add HttpContinueReadHandler in undertow transport handlers configuration to get it work, we better can support it OOTB.