Change in-product mentions from Duo Workflow to Duo Agent Platform

Problem

As laid out in &18255 the product name is changing from GitLab Duo Workflow to GitLab Duo Agent Platform. We need to ensure this is clearly communicated within the product.

Desired Outcome

There shouldn't be any mentions any more of Duo Workflow in the product, it should either reference the Agent Platform or Flows/Runs where appropriate as pointed out in &18255.