Add page for container registry under the package group

Why is this change being made?

The Package group owns several categories, among which is the Container Registry. We are now working on creating an onboarding template for engineers working on the Container Registry and noticed that we don't have a single place to direct new (and existing) team members to obtain additional information about the project (be that historical context or specific processes and tools).

This MR creates such a page under handbook/engineering/development/ops/package/container-registry and starts by adding historical context about the project.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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