Adding custom js enricher to validate stm

Fixes gitlab-org/gitlab#422449 (closed)

Added custom javascript enricher

In case stm is not present, it will move it to "bad" events queue and will not stall pipeline.

Added below function with base64 encoding.

function process(event) {
  if (!event.getDvce_sent_tstamp()) {
    throw "dvce_sent_tstamp is not defined";
  }
}

I have tested it in local devkit, it works fine there.

gitlab-org/gitlab#422449 (closed)