Add Gitee import button

What does this MR do and why?

Describe in detail what your merge request does and why.

We add Gitee import feature to JH side. We override app/views/projects/_import_project_pane.html.haml in jh directory before. However, we decided that this was not the best approach, so we added render_if_exists to render the Gitee import button on this page.

/cc @prajnamas

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