Install poetry-plugin-export, as it will not be installed by default in future poetry versions

[almet]

When generating the image with install/common/build-image.py, a warning is currently generated, telling us that the tool we currently use will not be included in future versions of poetry-export.

Warning: poetry-plugin-export will not be installed by default in a future version of Poetry.
In order to avoid a breaking change and make your automation forward-compatible, please install poetry-plugin-export explicitly. See > https://python-poetry.org/docs/plugins/#using-plugins for details on how to install a plugin.
To disable this warning run 'poetry config warnings.export false'

We want to make sure it's installed, (or to use a different mechanism if it makes more sense)