Register a custom date formatter used like build-in ones

Hi All,

In my index, I used a certain date format, for example - "format" : "yyyy-MM-dd HH:mm:ss.SSS", in multiple locations of field definitions in my type mappings. As this date format does not match any build-in ones, i just wonder if i can register such date formatter as something like mydate_time. And then use it like this - "format" : "mydate_time", in field definitions, so that i don't have to copy this long string - "yyyy-MM-dd HH:mm:ss.SSS", in many places, which also allows a better maintainability.