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
ASYNC_EVENT_ACTION_MAPPING = False
if get_bool_from_env("ASYNC_EVENT_ACTION_MAPPING", False):
    ASYNC_EVENT_ACTION_MAPPING = True
# Clickhouse Settings
CLICKHOUSE_TEST_DB = "posthog_test"
CLICKHOUSE_HOST = os.environ.get("CLICKHOUSE_HOST", "localhost")
CLICKHOUSE_USERNAME = os.environ.get("CLICKHOUSE_USERNAME", "default")
CLICKHOUSE_PASSWORD = os.environ.get("CLICKHOUSE_PASSWORD", "")
CLICKHOUSE_DATABASE = CLICKHOUSE_TEST_DB if TEST else os.environ.get("CLICKHOUSE_DATABASE", "default")
CLICKHOUSE_CA = os.environ.get("CLICKHOUSE_CA", None)
CLICKHOUSE_SECURE = get_bool_from_env("CLICKHOUSE_SECURE", not TEST and not DEBUG)
CLICKHOUSE_VERIFY = get_bool_from_env("CLICKHOUSE_VERIFY", True)
CLICKHOUSE_REPLICATION = get_bool_from_env("CLICKHOUSE_REPLICATION", False)
CLICKHOUSE_ENABLE_STORAGE_POLICY = get_bool_from_env("CLICKHOUSE_ENABLE_STORAGE_POLICY", False)
CLICKHOUSE_ASYNC = get_bool_from_env("CLICKHOUSE_ASYNC", False)
_clickhouse_http_protocol = "http://"
_clickhouse_http_port = "8123"
if CLICKHOUSE_SECURE:
    _clickhouse_http_protocol = "https://"
    _clickhouse_http_port = "8443"
CLICKHOUSE_HTTP_URL = _clickhouse_http_protocol + CLICKHOUSE_HOST + ":" + _clickhouse_http_port + "/"
IS_HEROKU = get_bool_from_env("IS_HEROKU", False)
KAFKA_URL = os.environ.get("KAFKA_URL", "kafka://kafka")
_kafka_hosts = KAFKA_URL.split(",")
KAFKA_HOSTS_LIST = []
for host in _kafka_hosts:
    url = urlparse(host)
    KAFKA_HOSTS_LIST.append(url.netloc)
KAFKA_HOSTS = ",".join(KAFKA_HOSTS_LIST)
POSTGRES = "postgres"