Fix release from #1860 (hotfix #1934).

- Cron job to send weekly email report is processed multiple times. Review scheduling process to send to only one worker.
- Implement mechanism to ensure each email is sent only once to each recipient.
- Improve the way the async task is processed by creating a separate task for each organization, instead of processing all organizations in a single task.
posthog/settings.py
JS_URL = os.environ.get("JS_URL", "http://localhost:8234/")
else:
    JS_URL = os.environ.get("JS_URL", "")
# This is set as a cross-domain cookie with a random value.
# Its existence is used by the toolbar to see that we are logged in.
TOOLBAR_COOKIE_NAME = "phtoolbar"
# SSL & cookie defaults
if os.environ.get("SECURE_COOKIES", None) is None:
    # Default to True if in production
    secure_cookies = not DEBUG and not TEST
else:
    secure_cookies = get_bool_from_env("SECURE_COOKIES", True)
TOOLBAR_COOKIE_SECURE = secure_cookies
SESSION_COOKIE_SECURE = secure_cookies
CSRF_COOKIE_SECURE = secure_cookies
SECURE_SSL_REDIRECT = secure_cookies
if not TEST:
    if os.environ.get("SENTRY_DSN"):
        # http
        sentry_sdk.init(
            dsn=os.environ["SENTRY_DSN"],
            integrations=[DjangoIntegration(), CeleryIntegration(), RedisIntegration()],
            request_bodies="always",
            send_default_pii=True,
        )
if get_bool_from_env("DISABLE_SECURE_SSL_REDIRECT", False):
    SECURE_SSL_REDIRECT = False
if get_bool_from_env("IS_BEHIND_PROXY", False):
    USE_X_FORWARDED_HOST = True
    SECURE_PROXY_SSL_HEADER = ("HTTP_X_FORWARDED_PROTO", "https")