gitlab-ci and readme need to be updated

Specify the correct location of the nginx-httpg_no_delegation.patch file in the script for installing openresty-voms in the devcontainer

The build-install-openresty-voms.sh script is copied in /usr/local/bin instead ~/bin.

Deleted the addition of ~/bin from PATH env variable.

All the file in assets used tu build the devcontainer are moved in library-script.

Modify the Dockerfile COPY directory

* To reduce the image dimension, two RUN commands are merged in one single layer.
* All packages are installed with a single command.
* remove cern and garr mirrors
* the clean commands are the last instructions in the layer
* sudo is installed only in the dockerfile

To create the vscode user, the provide_user.sh script is used. With this script the comand line appearance is improved with colors and branch informations