Conjugate VJP and JVP support

[CameronChurchwell]

VJP and JVP implementations for the conjugate primitive

Currently, the complex conjugate operation is not supported by the autograd because the underlying Conjugate primitive does not have vjp or jvp definitions. This PR adds those missing definitions.

I also added a few lines to the test_conjugate unit test in python/tests/test_ops.py that cover both vjp and jvp calls for conjugate. To my knowledge, no documentation changes are necessary.

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[angeloskath]

Looks great thanks!