Evaluate usage of 'ensurepip'

[tomuben]

Background

In #113 @Nicoretti suggested to use ensurepip instead of get-pip (the approach we use today).
This would have the advantage of being independent of an URL for installing pip(see #111).
However, @tkilias told me there were some issues in the past with ensurepip, for example one problem might be that an existing version of pip will not be replaced.

Acceptance Criteria

Validate if ensurepip can be used instead of get-pip:

1. Check if it works
2. Check if it replaces an existing version of pip