Add webserver option to limit client request payload size

[barchetta]

Add an option to limit the payload size of incoming requests. If an incoming request exceeds the maximum payload size then the server would return 413 Payload Too Large. This should work with both Content-Length and Transfer-Encoding: chunked.

Some examples from other HTTP servers:

• https://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size
• https://httpd.apache.org/docs/current/mod/core.html#limitrequestbody
• https://www.eclipse.org/jetty/documentation/current/configuring-form-size.html

It's understood that the Helidon WebServer is not intended to be a full featured tier 1 HTTP server. But this seems like a reasonable request to harden the webserver to help detect/avoid client bugs and defend against DoS attacks.

[spericas]

PR #2491