Add logging for rack attack events

Patch for issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/15612 and partial patch for https://gitlab.com/gitlab-com/support/issues/119.

Also related: https://gitlab.com/gitlab-org/gitlab-ce/issues/22527 

Adds logging for throttle and blacklist rack attack events to the production log.

@stanhu @MrChrisW

See merge request !7585