Investigate: Process webhook notifications for tag delete and create events

Context

The epic Container Registry GMAU: Track usage (&8213) proposes adding user-level data for the GitLab Container Registry. This data would help drive prioritization and investment in the Container Registry category.

The high-level plan for delivering this was outlined in https://gitlab.com/gitlab-org/gitlab/-/issues/364730#note_1058520288. This specific issue is part of Container Registry AMAU - Process data (&9234), which targets the "Process" stage of the outlined implementation plan.

Task - Investigation

As described in https://gitlab.com/gitlab-org/gitlab/-/issues/364730#note_1058520288, the first step is to process the already emitted (by the registry) and consumed (by Rails) registry webhook notifications for tag delete/create requests. This needs to be done on the Rails side.

These notifications already include the type of event, the target container repository, and the username. So they have all that Rails needs to consume and increment the respective (new) counters to track usage.

This issue is meant to be an investigation on how to implement the collection and processing of these events on the rails side to increment (new) counters for usage tracking.

The end goal is to count the number of users that have created or deleted container registry tags. It should be possible to aggregate these counters by month and week, so that we can know how many distinct users created/deleted tags per month and week.

For scalability reasons, this should likely be implemented with Redis counters, similar to how it was done for package registry events in Implement redis based package events tracking (#275942 - closed). Since this was done a few years ago, we should make sure this is still the best option. We should also involve Product Analysts in this conversation (see https://gitlab.com/gitlab-org/gitlab/-/issues/364730#note_1027217479).