Add Complete maturity target and update Lovable maturity target

Why is this change being made?

The cloud native installation currently has a maturity of Viable. It had a target of 2023 to reach Lovable. We should be more ambitious and aim for the cloud native installation to be Lovable by the end of 2020. We need to do further customer research to determine exactly what Lovable looks like, so the target of 2020/12 may need to be adjusted depending on the final definition.

In addition to adjusting the Lovable target, I'm adding an interim target of reaching a Complete maturity status. A Complete status is being defined in gitlab-org&2260 (closed) but is also subject to change based on customer feedback.

Does this MR meet the acceptance criteria?

Conformity

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

Related to Product#620 (closed)