make it easy to switch to python2 in edk2 containers

[AtomicFS]

I find myself often need to switch to python2 in older edk2 containers, but we can't just carper-change all of them. So either let's add new containers with python2 as default, or make it easy to switch (like a script for example).

[AtomicFS]

@MDr164 what do you think? Should we double the number of edk2 containers, or just make some switch script equivalent to:

apt remove -y python-is-python3
update-alternatives --remove python /usr/bin/python3
update-alternatives --install /usr/local/bin/python python /usr/bin/python2 100

We could also do this, but apt update would slow it down:

apt update
apt remove -y python-is-python3
apt install -y python-is-python2
update-alternatives --remove python /usr/bin/python3
update-alternatives --install /usr/local/bin/python python /usr/bin/python2 100