Update competitive landscape for package

Why is this change being made?

On the Package Registry direction page we have an overview comparing our supported package manager formats to some competitors. The issue is that the list does not include many of the formats that the universal package management tools, such as Artifactory, support.

The reason for this is that Artifactory supports many package manager formats that have simply never been requested by our customers and have very little community support. Our goal in the Package stage is to help our customers replace their existing vendor, not build every feature that our competition has built.

This MR adds a note that the list displays our most frequently requested and supported package manager formats and prompts them to open an issue if they'd like to suggest a new format. We also link them to our suggested contributions page.

Next iteration

I think this section of the page needs significant improvement. We should not be comparing ourselves to Artifactory/Nexus solely on supported formats but on use cases and features. In my June direction updates, I'll add more thought and context to this section. I think we can say more and still keep it concise and clear.

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
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • 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 relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.

For help with failing pipelines reach out in #mr-buddies in Slack