Provide context in JSF UI to Web UI migration

As a / an Studio user

• I want to be able to learn how migration works before triggering it
• I want to know how to check the migration result
• I want to give feedback on the feature so that devs can take it into account

Acceptance criteria
In the migration screen

• A message is shown on top of the page saying:
  Your current configuration can be migrated from JSF UI to Web UI. [Learn more](https://doc.nuxeo.com/studio/jsf-web-ui-migration)

• A message is shown below it:
  Want to tell us about your experience with this early access feature? [Give feedback](https://docs.google.com/forms/d/e/1FAIpQLSdoDfpJOnFwkxHAHOk5aq5KHh9myxF6fISugnMzVmvuQSp-fw/viewform?usp=pp_url&entry.1064623659=[user email address] in a new page)

• A message is shown in the previous migrations zone saying:
  Learn [how to review and merge migration changes](https://doc.nuxeo.com/studio/how-to-review-nuxeo-studio-configuration in a new page)