pricing: phase-2: Project Setting to set Default Deployment cluster size

[royendo]

Start a setting section on dev deployments; add hibernate settings here when ready

needs: #9120

replace dropdown with mange units modal with different wording for DEFAULT cluster size; this does not change existing deployments only net new ones.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!