Performance: enable delayed logging

Problem/Motivation

Currently, log messages are added to solr on every log() call. This also possibly establishes connection to solr anew, adding overhead to request processing.

Proposed resolution

Add an option to bulk-log all the messages in the end of request, only establishing the connection to Solr server if there are messages.

This has to be switchable, in order to be able to log messages when kernel crashes before termination.

Remaining tasks

Write the patch

User interface changes

New boolean "Delayed log" setting in solrlog.settings (on by default, no change for existing installations)