MDSD does not match :time value type

Fluentd maps `:time` data types to `Fluent::EventTime` in [Fluentd v1 official docs](https://docs.fluentd.org/configuration/parse-section#types-parameter). MDSD plugin only maps `Time` to `FT_TIME` in [fluentd plugin](https://github.com/Azure/fluentd-plugin-mdsd/blob/0.1.10/src/fluent-plugin-mdsd/lib/fluent/plugin/out_mdsd.rb#L146). I'd like to extend the mapping table with the `"Fluent::EventTime" => "FT_TIME"`. For whatever reason I'm not authorised to raise a PR, so here's an issue instead.