Branch from feature branch to release branch

Create release branch:

• manually for qtwebengine and qtscript, update also .gitmodules: https://codereview.qt-project.org/c/qt/tqtc-qt5/+/475114
• other repositories: Instructions: https://intranet.qt.io/pages/viewpage.action?spaceKey=QTRD&title=Branching+instructions

Restrict staging in release branch to release team only
Bump Version number in feature branch