Maturity and direction updates for the Package Registry

Why is this change being made?

As part of the monthly direction updates, this MR adjusts the maturity plan and direction page for the Package Registry. In addition to the changes here, I also opened the epic gitlab-org&2891, which includes details like JTBD and links to the issues.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what