give admins more warning before deleting channel

value

• we want to delete metadata associated with unused channels as frequently as possible to keep our users safe
• we also want to prevent deleting channels that people still wanted to use b/c they didn't receive or pay attention to the deletion notices we send before deleting
• this MR provides a design to extend the grace period we offer before deleting a channel and "nudge" users 3 times (instead of just 1) before actually deleting the channel

behavior

GIVEN a channel that scheduled for deletion

• WHEN 72 hours (3 days) pass from the deletion request being made
• THEN the system should delete the channel and notify admins, subscribers, and maintainers of the deletion (as it currently does)

GIVEN a channel scheduled for deletion

• WHEN {0,24,48} hours have passed from the deletion request being made
• THEN the admins of the channel receive a message that says `'Hello! This channel will be destroyed in {72,48,24} hours due to lack of use. To prevent it from being destroyed, send INFO within the next {72,48,24} hours. If you would like to destroy the channel right now, respond with DESTROY. For more info, visit https://signalboost.info/how-to.',

implementation notes

for increased deletion grace period

• edit config.jobs.channelDestructionGracePeriod to be 3 days (in millis)

for nudging

• add a lastNotified timestamp field to the destructionRequest model
• add a destructionRequestsRepository#getNotifiableDestructionRequests function
  • this returns all destruction requests that:
    • createdAt is more than 3 days ago
    • lastNotified is more than 1 day ago
• when the processDestructionRequests job runs:
  • in addition to calling getMatureDestructionRequests and destroying them, also call getNotifiableDestructionRequests
  • send notifications to admins of all channels returned from this query