create quantum_fourier_transform (#6682)

* create quantum_fourier_transform

This is part of the #Hacktoberfest.
I build the quantum fourier transform for N qubits. (n = 3 in the example)
Best,
Kevin

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* Update q_fourier_transform.py

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* Add the doctest!

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* Update q_fourier_transform.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <[email protected]>