Search in Launchpad by PR URL. GitHub (#3543)

[sergeibbb]

Description

When I copy and paste a PR URL directly into the input box on the main step, it should search for that PR

Checklist

• [x] I have followed the guidelines in the Contributing document
• [x] My changes follow the coding style of this project
• [x] My changes build without any errors or warnings
• [x] My changes have been formatted and linted
• [ ] My changes include any required corresponding changes to the documentation (including CHANGELOG.md and README.md)
• [x] My changes have been rebased and squashed to the minimal number of relevant commits (please, don't squash, I think it's to big to be squashed in 1 commit).
• [x] My changes have a descriptive commit message with a short title, including a Fixes $XXX - or Closes #XXX - prefix to auto-close the issue that your PR addresses