Bound on QCQP

[blegat]

Add example on how to get a bound on a QCQP as done in https://github.com/Shuvomoy/BnB-PEP-code/

cc @Shuvomoy

[Shuvomoy]

@blegat, An illustrative example is available at the blogpost https://shuvomoy.github.io/blogs/posts/Automatic_sdp_relaxation_of_QCQP_in_JuMP_Julia/