[books] Allow timezone changes when importing from KOReader

Turns out you need a city-based timezone for DST stuff to work properly.
The US/Eastern timezone doesn't mess with DST because it can be so wonky
in different regions. So while we fix timezone defaulting to a
DST-friendly timezone too.

vrobbler/settings.py

@@ -92,7 +92,7 @@ DEFAULT_TASK_CONTEXT_TAGS = [
 
 DEFAULT_AUTO_FIELD = "django.db.models.BigAutoField"
 
-TIME_ZONE = os.getenv("VROBBLER_TIME_ZONE", "US/Eastern")
+TIME_ZONE = os.getenv("VROBBLER_TIME_ZONE", "America/New_York")
 
 ALLOWED_HOSTS = ["*"]
 CSRF_TRUSTED_ORIGINS = [
@@ -111,7 +111,7 @@ CELERY_TASK_ALWAYS_EAGER = (
 )
 CELERY_BROKER_URL = REDIS_URL if REDIS_URL else "memory://localhost/"
 CELERY_RESULT_BACKEND = "django-db"
-CELERY_TIMEZONE = os.getenv("VROBBLER_TIME_ZONE", "US/Eastern")
+CELERY_TIMEZONE = os.getenv("VROBBLER_TIME_ZONE", "America/New_York")
 CELERY_TASK_TRACK_STARTED = True
 
 INSTALLED_APPS = [