feat(e2e): add QEMU test

This uses the hermetic QEMU toolchain, the QEMUStrategy and the the QEMU images to create an end-to-end test for QEMU. Currently, only AMD64 is covered, we'll add ARM64 later.

This test should take between 90-120 seconds to run without cache, most of which is waiting for the QEMU image to boot. There's no visual feedback (not even with --test_output=streamed), which is something we might want to try to improve in the future.

There's an intermittent failure where QEMU tries to write to /var/tmp, which can be worked around locally by passing the --sandbox_tmpfs_path=/var/tmp flag. A proper fix will be provided in a future MR.