Pin Qiskit to <2 in next release

[edoaltamura]

Summary

Pinning Qiskit<2 will avoid breaking changes to affect current installations. This potential effect was raised in #897. The constraint can be removed when QML achieves full compatibility with Qiskit 2.

[woodsp-ibm]

I am wondering - in the requirements.txt already exists a version limit for qiskit

qiskit>=1.0
scipy>=1.4
numpy>=1.17
scikit-learn>=1.2
setuptools>=40.1
dill>=0.3.4

Would it be better to keep the version restrictions in one place especially since its a direct dependent i.e. qiskit>=1.0,<2.0. I also notice that there is a version limiting on numpy while the constraints.txt has something different.