Implement zoneinfo support to drop dependency to pytz

Zoneinfo was introduced within python 3.9.

The support of pytz will be removed within RHEL 10 [1].

2023.2 (bobcat) will move our testing runtime to py3.9 and py3.10
so we want to see pytz removed within this series.

tzdata is required at runtime in our gates, because, by default,
zoneinfo uses the system’s time zone data if available; if no system
time zone data is available, the library will fall back to using the
first-party tzdata package available on PyPI. Apparently our gates have no
time zone data available nor tzdata installed by default because we get the
following error without tzdata installed [3]:
`ModuleNotFoundError: No module named 'tzdata'

So I prefer to add tzdata in our requirements to avoid runtime failure
related to time zone and ensure that time zone are always available.

[1] https://issues.redhat.com/browse/RHEL-219
[2] https://review.opendev.org/c/openstack/governance/+/872232
[3] https://zuul.opendev.org/t/openstack/build/0a1576775e894b09bc31269fea00ba03/log/job-output.txt#1445`

Depends-on: https://review.opendev.org/c/openstack/requirements/+/875854
Change-Id: I1f88bdadc68bfa726eac1da1c5824c1ed352ad98

oslo_utils/timeutils.py

@@ -22,9 +22,9 @@ import datetime
 import functools
 import logging
 import time
+import zoneinfo
 
 import iso8601
-import pytz
 
 from oslo_utils import reflection
 
@@ -225,8 +225,8 @@ def unmarshall_time(tyme):
     if tzname:
         # Need to handle either iso8601 or python UTC format
         tzname = 'UTC' if tzname == 'UTC+00:00' else tzname
-        tzinfo = pytz.timezone(tzname)
-        dt = tzinfo.localize(dt)
+        tzinfo = zoneinfo.ZoneInfo(tzname)
+        dt = dt.replace(tzinfo=tzinfo)
     return dt
 
 

releasenotes/notes/implement-zoneinfo-to-remove-pytz-fba6f70db09ecdb8.yaml

@@ -0,0 +1,6 @@
+---
+other:
+  - |
+    Implement zoneinfo to allow us to remove pytz's dependency. zoneinfo
+    was introduced by python 3.9, and the series 2023.2 (bobcat) set py39
+    as the minimal supported runtime, so we are able to remove pytz.

requirements.txt

@@ -5,9 +5,9 @@
 
 iso8601>=0.1.11 # MIT
 oslo.i18n>=3.15.3 # Apache-2.0
-pytz>=2013.6 # MIT
 netaddr>=0.7.18 # BSD
 netifaces>=0.10.4 # MIT
 debtcollector>=1.2.0 # Apache-2.0
 pyparsing>=2.1.0 # MIT
 packaging>=20.4 # BSD
+tzdata>=2022.4 # MIT