Fix commented-out RequestLog in jetty.xml to use non-deprecated class

Currently the jetty request logging is disabled (commented out).

But it can be useful, e.g. since it uses a standard logging format and there are tools to analyze it by default. Also it can be used to detect some attacks not otherwise logged anywhere else, since they don't make it to solr servlet: requests blocked at the jetty level (invalid/malformed requests, ones filtered by jetty IP filtering, etc).

We should switch it from the deprecated NCSARequestLog class, instead to use the CustomRequestLog with either NCSA_FORMAT or EXTENDED_NCSA_FORMAT.

Deprecated.
use CustomRequestLog given format string CustomRequestLog.EXTENDED_NCSA_FORMAT with a RequestLogWriter