Add initial qsim CUDA version expectation op

[jaeyoo]

This is the first draft version which worked for the google internal infrastructure.

We need to modify this code as the following steps:

1. Update & polish the code working for the external environment. (e.g. fix build error, naming, remove unused codes and commented code lines etc.)
2. Update the gpu_benchmark.py file to see the better result on the external gpu environment.
3. Add qsim cuQuantum version gpu op for expectation op.

[jaeyoo]

@Sinestro38 Please take this PR for your implementation

[MichaelBroughton]

This looks awesome @jaeyoo ! Can we test this on github actions with GPU or add a kokoro job to do our GPU testing ?

[jaeyoo]

Sure Michael! Thank you so much :) I am working on designing Kokoro-based GPU CI testing infra. My ETA is early June. Let's sync it together at our next meeting.