Implement find-and-replace creation UI

Created by: courier-new

The scope of this issue is the UI for the find-and-replace workflow based on the Figma designs:

• When the user clicks "Preview Pull Requests" from search, they are taken to a new page (/create/find-and-replace?) with an extended configuration form (reuse all the UI elements from server-side execution) for inputting the details of their batch change and changesets.
  • The page needs to remember the compute search query + mode, find term, and replace term it came from.
  • All of the fields are required
  • The author email + username are pre-filled with the default commit author email + username (can we get this over GraphQL already?)
  • The batch change name should have the same validation as in server-side
  • The branch name should have validation that it's a valid branch name
  • The email should probably have validation that it's email-y
  • Cancel takes the user back to their search query
• When the user has filled out the configuration and clicks "Preview Pull Requests" again, whatever API interaction from https://github.com/sourcegraph/sourcegraph/issues/40120 happens to create the batch change, batch spec, and changesets. The user waits on this page (or is taken to another loading page?) until the changeset creating job is complete.
• When the changeset creating job is complete, the user is taken to the preview page to see the created changeset specs.