Create command line monitor for internal events tracking

What does this MR do and why?

Adds a script that makes it way easier to monitor which metrics are updated and which Snowplow events are triggered.

Currently it takes a lot of work and looking around in the Service Ping payload to verify that metrics got updated. This script removes that pain point in many cases.

Video demo:

command_line_monitor_short

This script does not have any test and the code show very clearly that this is a proof of concept.

In the spirit of iterating and providing value as early as possible, I suggest that we merge it now and address the test and code structure another issue: #426630

How to set up and validate locally

1. Open two terminals
2. Start the monitor in Terminal 1 by running bin/rails runner scripts/internal_events/monitor.rb i_code_review_saved_replies_use i_code_review_saved_replies_create
3. Start a Rails console in Terminal 2 by running gdk rails console
4. Trigger an event in 2 by executing: Gitlab::InternalEvents.track_event("i_code_review_saved_replies_create", user: User.last, namespace: Namespace.last)
5. Verify in Terminal 2 that:
   1. The metrics defined on i_code_review_saved_replies_create increased (If you didn't already trigger an event with this user previously)
   2. A new Snowplow event appeared on the list with the correct event_name, user_id and namespace_id

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.