Full testing environment for the releasing pipeline

We need a complete setup to test all packaging-related changes so that production jobs are not affected whenever changes are tested.

This includes servers, services, and packaging scripts.

Overall releasing system picture here: https://intranet.qt.io/display/QTRD/Releasing+system+details

Objective:

• 'Dev' branch in the use in tqtc-qtsdk.git
• Scripts from qtsdk.git moved under tqtc-qtsdk.git -> https://bugreports.qt.io/browse/QTQAINFRA-5500

• Master branch is used in the production. 'dev' is merged to 'master' at maintenance date
• We have staging jenkins in the use as well