Micropip should be able to process requirements files

[hoodmane]

🚀 Feature

We should have a micropip version of pip install -r requirements.txt. Maybe micropip.install(requirements_file="some/path").

[rth]

We should probably nudge users toward using some form of a lock file instead of a requirement.txt file, but I suppose it still makes sense to support requirements.txt files for existing projects.