EE BE Improve the GitHub and Gitea import feature table interface

What does this MR do?

This is the EE backend to vue-ify the import feature for github and gitea.

Please view the Table of MRs.

This MR specifically:

• Ports changes from CE BE MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24606

• Removes markup in githubish_status.html.haml template and a test in new_project_spec.rb that depends on this markup. This is to get CI working. The FE is added in the EE FE MR which restores these tests. Please view the Table of MRs to find the FE MRs.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14010

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer