Moved build phase 2 develop and test to outcome and activities

Why is this change being made?

This change moves the Build Phase 2 - Develop and Test from a detailed process description to an outcome and activity focused section. This means rather than listing how labels need to be applied it focuses on the why and the expected outcomes.

This also shifts workflowready for development and Deliverable labels and motions to Build Phase 1 - Plan. This phase is all about a team executing on building a feature after it's been prioritized and committed to for a milestone.

Closes #9110 (closed)

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.