Feature request: support date-based table names in logstash-input-azurewadtable

There are many valuable metrics available in tables like `WADMetricsPT1MP10DV2S20160813` but the table name suffix changes with the date every 10 days.

At the moment, retrieving data from these tables via the `logstash-input-azurewadtable` plugin would require regenerating the logstash configuration files every 10 days and restarting the logstash process.

It would be great if the plugin supported a place holder value in `table_name` config parameter which would be replaced at query time with the appropriate date which aligns to the 10-day block beginning immediately before the `last_timestamp`.