Make whether to take min or max version interpreter configurable in pex CLI

[CMLivingston]

During interpreter selection portions of the pex codebase (for building pexes and for running them), the logic is currently selecting the lowest-version interpreter when multiple compatible interpreters are present.

A useful feature would be to have a command line flag that allows the user to specify whether to take the min or max versioned interpreter amongst multiple compatible interpreters. This would allow greater flexibility in a given organization's interpreter management strategies.

A clear example of when this filtering occurs is in the interpreter selection logic of the build_pex function in bin/pex.py.