Log event when new editors reach edit milestone

Log an event when an editor who registered in the last 30 days makes their
first, fifth, tenth, twenty-fifth, fiftieth or hundredth edit.

See <https://meta.wikimedia.org/wiki/Schema:NewEditorMilestone>.

Change-Id: Ia6f758068ed1036014de105e3ab34b932149c13b
Merge "Log event when new editors reach edit milestone"