Update deployment defaults with project init

[cicdw]

Similar to #9145 this PR updates recipe defaults to guide users to healthy deployments as quickly as possible. In this case, anytime a user uses a docker-based recipe, we default to using a job variable that references the image_name output of build_docker_image.

Example

Running prefect project init --recipe docker now produces the following work pool section:

work_pool:
  job_variables:
    image: '{{ image_name }}'
  name: null
  work_queue_name: null

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• This pull request includes tests or only affects documentation.
• This pull request includes a label categorizing the change e.g. fix, feature, enhancement, docs.

[netlify]

✅ Deploy Preview for prefect-docs-preview ready!

Name	Link
🔨 Latest commit	ffb66ec
🔍 Latest deploy log	https://app.netlify.com/sites/prefect-docs-preview/deploys/643052577ee8c30008058000
😎 Deploy Preview	https://deploy-preview-9146--prefect-docs-preview.netlify.app/api-ref/prefect/cli/root
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[serinamarie]

LGTM :)

[desertaxle]

LGTM!