Make maxFormContentSize and maxFormKeys configurable in Knox's embedded Jetty server

There are certain deployments, where increasing the maxFormContentSize configuration is required because the default 200kB is not enough in POST forms.

Jetty checks these configurations on two levels: first in the context, and then, if the context is not available (it's a very rare non-typical Jetty deployment), looks it up in the server's attributes:

The form content that a request can process is limited to protect from Denial of Service attacks. The size in bytes is limited by {@link ContextHandler#getMaxFormContentSize()} or if there is no context then the "org.eclipse.jetty.server.Request.maxFormContentSize" {@link Server} attribute.

The number of parameters keys is limited by {@link ContextHandler#getMaxFormKeys()} or if there is no context then the "org.eclipse.jetty.server.Request.maxFormKeys" {@link Server} attribute.

Please note that these configurations are controlled by the System properties called org.eclipse.jetty.server.Request.maxFormKeys and org.eclipse.jetty.server.Request.maxFormContentSize.

This Jira is about to override them in gateway-site.xml.