Container Registry: Add link to epic for lowering the cost of storage to direction page

Why is this change being made?

We were linking to more specific issues, but did not call out the epic of epics that captures all of the work we are planning to help our customer and gitlab.com lower the cost of storage of for the container registry. This MR adds that link + description

Conformity

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