python version tag to support a 3.8 based 14.0 and onward

[dnplkndll]

Are we interested in promoting a tag for python 3.8 to the docker images? We starting to see the need with some python modules. I was not sure how to PR that change with the build CI involved.
@JordiBForgeFlow

[yvaucher]

For instance we created a separate build for 12.0-buster (563e389)

We could create a tag 14.0-py38

But note that we aim to provide images mainly for the versions officially supported by Odoo.