Parse As Simple Datetime Directive : Universal directive to support all date, datetime and epoch timestamp format

ParseTimestamp directive supports a single timeunit for all epoch values in the same field. The timeunit has to be mentioned explicitly for parsing seconds or nanoseconds unit.

Proposing a new directive to fix this:
1. A universal ParseSimpleDatetime directive to support date, datetime and epoch timestamp format and convert into a standardised UTC zoned datetime format.
2. Records with empty field values not skipped or sent to error collector. Instead empty values parsed as null.
3. Epoch time unit(ie. seconds, milliseconds, nanoseconds) identified based on epoch value length. Therefore, supports multiple epoch timeunit values in a single field.