scripts: add allocate_vram script

[psychedelicious]

Summary

Allocates the specified amount of VRAM, or allocates enough VRAM such that you have the specified amount of VRAM free.

Useful to simulate an environment with a specific amount of VRAM.

Related Issues / Discussions

Wrote to help troubleshoot #6613

QA Instructions

Try it out if you like. It works fine for me on linux.

Merge Plan

n/a

Checklist

• [x] The PR has a short but descriptive title, suitable for a changelog
• [ ] Tests added / updated (if applicable)
• [ ] Documentation added / updated (if applicable)