Simplify the CI pipeline for docker images repo

Right now, all builds related to docker are executed in docker-images repository. We should break this in form of a "Gitlab project chain". So, this is how the builds should happen:

1. SRC repo - hello-world-qtcloud
2. Qt6Base repo - Qt6 docker image
   1. Qt6Base+WASM
   2. Qt6Base+Android_x86
   3. Qt6Base+Android_x86_64
   4. Qt6Base+Android_arm7
   5. Qt6Base+Android_arm8
   6. Qt6Base+Yocto
3. Qt5Base repo - Qt5 docker image
   1. Qt6Base+Android

All of these projects should have the SRC repo as a git-submodule and have separate .gitlab-ci.yml which triggers relevant QtDockerBuild based on the configuration. 

As a proof of concept, it is OK to do this with python scripts (and not docker images) where SRC creates python module "HelloWorld", which is imported in QtBase as "HelloWorldQt" and in Wasm and Android images as "HelloWorldQt+Wasm", "HelloWorldQt+Android".