Add `pending` message data to daily and user_daily stats

[heyitsmebev]

Currently, the Recent Activity table displays only the counts for delivered and failed messages. We aim to include the count of pending messages to provide a clearer representation of the daily messages sent.

Backend work:

Please update these endpoints to also have "pending" count
get_service_notification_statistics_by_day
"/service/{0}/statistics/{1}/{2}".format(service_id, start_date, days)
get_user_service_notification_statistics_by_day
/service/{0}/statistics/user/{1}/{2}/{3}".format(service_id, user_id, start_date, days),

Frontend work:

Display pending stats to chart

[heyitsmebev]

@jonathanbobel researching/providing color options for pending that is accessible
@heyitsmebev will coordinate to get "pending" into the endpoint with backend dev and update the chart

[heyitsmebev]

Note to bev: fix this pending bar that is out of table

[heyitsmebev]

Note to bev:
These pending numbers are not always the same.
One is based on the count based on notification status = pending, created, and sending.
The other pending is based on requested - delivered - failed = pending

• Do I want to make them the same? Which method of calculations do I want to base them on?
  
• Does the notification_status account for all notifications with a pending status from multiple jobs within a service?
  Update: Two jobs have started processing, but the notification status count is accounting for the pending status of only one job. The job that it counts for does show up accurate in both pending within the endpoint and notification_sending on the job's page

[heyitsmebev]

requested and notification_count are different numbers. Because they are different, the job page will show a notification_count of 500, while the dashboard (using the daily stats endpoint) will display the value of requested as it updates in _update_statuses_from_row. The requested value is slow to retrieve than notification_count.