Enhance performance for ISO8601 in convertTimestamp morphline command

Consider adding a fast path to convertTimestamp command for ISO8601 (on input) as well as the ISO8601 flavor with millis expected by Solr (on output). Before doing so measure how much this helps wrt. performance.

For example via manually shading the corresponding jackson utils:

com.fasterxml.jackson.databind.util.ISO8601DateFormat and in particular com.fasterxml.jackson.databind.util.ISO8601Utils.format(Date date, true)