Add a warning with potential consequences before initiating the upgrade

[prilr]

[github-actions[bot]]

Thank you for contributing to the Leapp project!

Please note that every PR needs to comply with the Leapp Guidelines and must pass all tests in order to be mergable. If you want to re-run tests or request review, you can use following commands as a comment:

• leapp-ci build to run copr build and e2e tests in OAMG CI
• review please to notify leapp developers of review request

Please open ticket in case you experience technical problem with the CI. (RH internal only)

Note: In case there are problems with tests not being triggered automatically on new PR/commit or pending for a long time, please consider rerunning the CI by commenting leapp-ci build (might require several comments). If the problem persists, contact leapp-infra.