feat: Add LCG view and ATLAS AnalysisBase examples

[matthewfeickert]

Add full examples of use with LCG view and ATLAS AnalysisBase examples. For greater similarity in workflow to a normal use of python3 -m venv use cvmfs-venv as a subshell command and then source the created virtual environment.

* Add example using LCG view 102.
* Add example using ATLAS AnalysisBase v22.2.113.
* In these examples use cvmfs-venv as command that does not need to
  be sourced to make it more similar to how one would use a normal Python
  virtual environment.