fix(python-builder): [part 1] Replace continuumio/miniconda3 with condaforge/miniforge3 WITHOUT upgrades in python-builder image

[tyndria]

What

Summary of changes

• Replaced default channel image with the community-managed image.
• Remove explicit git installation as it's already a part of the used image

Checklist

• Added/updated unit tests
• Added/updated documentation
• Checked for typos in variable names, comments, etc.
• Added licences for new files

Testing

• Executed python_lint GH workflow locally with the new private image using act - working ✅
• Executed python_tests GH workflow by building the image inside the GH runner - output here - passed ✅
• Pushed python package to the pypi test index from the python-builder container - ✅

Next steps

• Push the new image to the seldonio hub
• Update the image tag in the workflows and makefiles (incl. run_python_builder command)

After we upgrade python in tests, we could upgrade python and conda version in this Dockerfile (cc @vtaskow)

[tyndria]

I believe it's better to move to the pipx installation of poetry after we upgrade python and the base condaforge/miniforge3 image, so we would get rid of this line
cc @vtaskow

[tyndria]

We would need to upgrade conda and python here after tests are upgraded
cc @vtaskow

[tyndria]

We would need to upgrade this image after python tests are upgraded
cc @vtaskow

[tyndria]

This is for testing purposes only (to test workflow after we push the image)