Add Telemetry for tracking Vault Integration Users

Problem to solve

As a data informed product team, we need to understand how the paid tier features are performing and one way to do this is to instrument usage pings and snowplow events for tracking usage. We need to instrument Action Monthly Active Users for all GitLab Starter, GitLab Premium and GitLab Ultimate tiers on both SaaS and Self-managed instances.

Project Management MAU Definition

The sum of all unique users that created a CI job with secrets configured over a given period of time.

Proposal

Add telemetry for Users running pipelines that have a HashiCorp Vault Variable implemented per the guidelines: https://docs.gitlab.com/ee/development/telemetry/ for both

1. https://docs.gitlab.com/ee/development/telemetry/usage_ping.html
2. https://docs.gitlab.com/ee/development/telemetry/snowplow.html (#235758 (comment 440725696))

Usage Ping

We'll use Redis HLL counters to track Ci jobs created that have (Vault) secrets configured - !46515 (merged). See here why we decided not to count these in the database - #235758 (comment 440460394).