Add support for Python 3.12 (Qiskit/qiskit#11262)

* Add support for Python 3.12

Python 3.12.0 was released on 10-02-2023, this commit marks the start of
support for Python 3.12 in Qiskit. It adds the supported Pythonv ersion
in the package metadata and updates the CI configuration to run test
jobs on Python 3.12 and build Python 3.12 wheels on release.

Fixes: Qiskit/qiskit#10887

* Add release note

* Avoid deprecated `datetime.datetime.utcnow()` usage

In Python 3.12 `datetime.datetime.utcnow()` has been deprecated, being
replaced by: `datetime.datetime.now(datetime.UTC)`. This commit updates
the usage of `utcnow()` to follow the new convention.

* Adjust UTC usage to support Python 3.8

The recommended alternative for using utcnow() in the deprecation
warnings emitted by Python 3.12 are not compatible with Python 3.8. The
datetime.UTC alias was not added to Python until Python 3.11. To ensure
that the code is compatible with Python < 3.11 this commit updates all
the usage of datetime.UTC to use datetime.timezone.utc instead, which is
what datetime.UTC aliases to in Python >=3.11.

qiskit_ibm_runtime/fake_provider/fake_backend_v2.py

@@ -42,7 +42,7 @@ def __init__(self):
             None,
             name="FakeV2",
             description="A fake BackendV2 example",
-            online_date=datetime.datetime.utcnow(),
+            online_date=datetime.datetime.now(datetime.timezone.utc),
             backend_version="0.0.1",
         )
         self._qubit_properties = [
@@ -116,7 +116,7 @@ def __init__(self, bidirectional=True):
             None,
             name="Fake5QV2",
             description="A fake BackendV2 example",
-            online_date=datetime.datetime.utcnow(),
+            online_date=datetime.datetime.now(datetime.timezone.utc),
             backend_version="0.0.1",
         )
         qubit_properties = [
@@ -188,7 +188,7 @@ def __init__(self):
             None,
             name="FakeSimpleV2",
             description="A fake simple BackendV2 example",
-            online_date=datetime.datetime.utcnow(),
+            online_date=datetime.datetime.now(datetime.timezone.utc),
             backend_version="0.0.1",
         )
         self._lam = Parameter("lambda")

qiskit_ibm_runtime/fake_provider/fake_mumbai_v2.py

@@ -39,7 +39,7 @@ def __init__(self):
         super().__init__(
             name="FakeMumbaiFractionalCX",
             description="A fake BackendV2 example based on IBM Mumbai",
-            online_date=datetime.datetime.utcnow(),
+            online_date=datetime.datetime.now(datetime.timezone.utc),
             backend_version="0.0.1",
         )
         dt = 0.2222222222222222e-9