Optionalall_boolean, optional, default to false, tells the client whether to only display dates for starts_at and ends_at
announcement content
Optionalends_datetime, optional, default to null, the time when the announcement will become inactive (no longer displayed to users); if it is null, the announcement will be active until an admin deletes it
Optionalstarts_datetime, optional, default to null, the time when the announcement will become active (displayed to users); if it is null, the announcement will be active immediately