Add ability to specify custom Handler in Jetty configuration file

[invviz]

Add ability to specify custom Handler in Jetty configuration file

[andreysubbotin]

For QA: Release 7.0, 7.1 and master.

[invviz]

For QA: Original forum topic: https://www.cuba-platform.com/discuss/t/gzip-compression-on-jetty/9267

It is necessary to verify that the application built using uberjar uses the handlers defined in the configuration file.
Example of the jetty configuration xml:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure_9_0.dtd">

<Configure id="Server" class="org.eclipse.jetty.server.Server">
    <Call name="addConnector">
        <Arg>
            <New class="org.eclipse.jetty.server.ServerConnector">
                <Arg name="server">
                    <Ref refid="Server"/>
                </Arg>
                <Set name="port">8090</Set>
            </New>
        </Arg>
    </Call>
    <Call name="insertHandler">
        <Arg>
            <New id="GzipHandler" class="org.eclipse.jetty.server.handler.gzip.GzipHandler">
                <Set name="includedMethods">
                    <Array type="String">
                        <Item>GET</Item>
                        <Item>POST</Item>
                    </Array>
                </Set>
            </New>
        </Arg>
    </Call>
</Configure>

In this example, the server should gzip all the responses.