[Import by URL] Migrate retry logic to Vue form

Issue #566389 (closed) rolled out the feature flagged import_by_url_new_page on production. Users when creating a new project via URL import are redirected to the Vue form.

However, there is some old retry logic that leads the user to the old form. Specifically, user is taken to app/views/projects/no_repo.html.haml and can click on Import repository, which takes them to app/views/projects/imports/new.html.haml

When an import fails, a project is automatically created without a repository and the user is prompted to import a repository. The form rendered in app/views/projects/imports/new.html.haml seems to account for the scenario where a project already exists and the user needs to import a repository. But the new URL import form does not seem to. So we cannot yet delete app/views/shared/_import_form.html.haml and ee/app/views/shared/ee/_import_form.html.haml and replace with the Vue form.

Acceptance criteria

• When an import fails and a project was already created, any prompts to retry the URL import should lead the user to a simplified Vue version of app/views/shared/_import_form.html.haml that is just for retries)
• It has been verified whether the shared '_import_form's are used anywhere else, and if not we can delete the form

Follow up Tickets

#592990 -> Adds alerts