Ping URL for measuring arbitrary data

Description

It would be extremely helpful if GitLab could help measuring arbitrary data, for instance whenever someone presses a certain button in my iOS app.

Competitors in this space require libraries and complex setup, I think we can do something much more simple with GitLab.

Proposal

Have a simple URL you can ping with some meta data/ping, to be able to record a data point.

For instance, I would ping gitlab.com/ping?token=ABCEF&project=gitlab-org/gitlab-ce&action=buttonPressed and this would be recorded in prometheus something like

{ "ping": 
  {
    "project": "gitlab-org/gitlab-ce"
    "action": "buttonPressed",
    "created_at": "23:32pm etc"
  }
}

Ideally, you'd be able to specify both sides of the key/value, but if not we could have a set amount of placeholders (like action).

A MVC would be to just have the ping address per project, so you can record a single type of event easily.

Links / references

/cc @gl-product @sytses