Add Lua filter to get metrics from auth messages

This filter sends the following multi-value metrics every minute:

- authentications_total, these counters reset to zero when the filter
  is restarted
  - all: the total number of authentications
  - success: the total number of successful authentications
  - failed: the total number of failed authentications
- authentications_rate
  - all: authentications per second in the last minute
  - success: successful authentications per second in the last minute
  - failed: failed authentications per second in the last minute
- authentications_percent
  - success: percentage of successful authentications in the last minute
  - failed: percentage of failed authentications in the last minute

Change-Id: Ia54ff110512e249d70d6568a4633da42748d45f5
2 files changed