Fix bug with different number of pages in different timezones (#36)

Fix bug with missing timezone, due to which `pull_alerts.py` print
different number of pages in different timezones.

The problem is that the `datetime.now()` object takes the local time,
but doesn't add information about the timezone, as a result, pagerduty
doesn't know from what time to collect pages and therefore uses some
default timezone, because of this, `pull_alerts.py` script will print
different number of pages in Europe and USA.

To fix this, we need to add information about the timezone, and **it
doesn’t matter** which timezone [will be
there](https://github.com/lyft/opsreview/pull/36/files#diff-0052311b4eedfd69118e059e6a7e4339d465ae632361809321aa302084769d7cR52),
for any time zone, absolute time will remain the same.

All the screenshots below were taken ~at the same time (5:30 AM,
Pacific).






**Without fix**:
Local time - Europe/Minsk:
                                                            Local
time - America/Los Angeles
<img alt="local - minsk, pacific 5 30"
src="https://github.com/lyft/opsreview/assets/45463018/088d3afc-997b-4b90-b8de-3b7dcba02b20"
width="398" height="186" > <img alt="local - los angeles, pacific 5 30
png"
src="https://github.com/lyft/opsreview/assets/45463018/898b57fd-56cc-4574-818e-57fe7b29748b"
width="398" height="186">
As you can see, the number of pages is different (18 vs 22), even though
the script run at the same time.
&#10;
&#10;
&#10;
**With fix** (test with
`datetime.now(tz=ZoneInfo("America/Los_Angeles"))` in code):
Local time - Europe/Minsk:
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Local
time - America/Los Angeles
<img alt="local - minsk, pacific 5 30"
src="https://github.com/lyft/opsreview/assets/45463018/cc925a91-28d2-4000-bb06-268c93554589"
width="398" height="186" > <img alt="local - los angeles, pacific 5 30
png"
src="https://github.com/lyft/opsreview/assets/45463018/7cc7e999-faaa-49fa-b143-95617576945d"
width="398" height="186">

**With fix** (test with `datetime.now(tz=ZoneInfo("Europe/Minsk"))` in
code):
Local time - Europe/Minsk:
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Local
time - America/Los Angeles
<img alt="local - minsk, pacific 5 30"
src="https://github.com/lyft/opsreview/assets/45463018/354e21ea-78aa-4855-a0a8-80c8b8d57b56"
width="398" height="186" > <img alt="local - los angeles, pacific 5 30
png"
src="https://github.com/lyft/opsreview/assets/45463018/3b15a1db-e960-4937-8115-6cce651d7fd4"
width="398" height="186">

As you can see, the number of pages is always the same (22).

pull_alerts.py

@@ -49,7 +49,7 @@ def recent_incidents_for_services(services, time_window):
     try:
         recent_incidents = list(pagerduty_service.incidents.list(
             service_ids=service_ids,
-            since=datetime.now() - time_window
+            since=datetime.now(tz=LOCAL_TZ) - time_window
         ))
         return recent_incidents