Add deprecation warning on use of qiskit.IBMQ (Qiskit/qiskit#8080)

* Add deprecation warning on use of qiskit.IBMQ

With the pending release of the qiskit-ibm-provider that superscedes the
qiskit-ibmq-provider package. The qiskit-ibmq-provider is now deprecated
and will be retired/archived in the future. In coordination with that
this commit deprecates the lazy loading fixture qiskit.IBMQ and removes
documentation references to qiskit-ibmq-provider in the repo.

* Fix typos

Co-authored-by: Jim Garrison <[email protected]>

* Remove superfluous warnings

* Add pip to warning message

* Fix lint

* Update references to qiskit.IBMQ

* Add release note

* Add back ibmq_mock.py file

* Add link to the migration guide in release note

Co-authored-by: Jim Garrison <[email protected]>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit_ibm_provider/fake_provider/__init__.py

@@ -70,7 +70,7 @@
 
     .. code-block:: python
 
-        from qiskit import IBMQ
+        from qiskit.providers.ibmq import IBMQ
         from qiskit.providers.aer import AerSimulator
 
         # get a real backend from a real provider