Timer-based functions

[svanimpe]

Various features (such as sending out notifications) need to be automated to run at certain times. This requires support for timers.

While it is possible to implement this in the main application, it's probably easier and cleaner to go serverless and use IBM Cloud Functions. This would work as follows:

• The main application provides API endpoints that implement the actual functionality.
• Small functions that call these endpoints are deployed to IBM Cloud Functions.
• These functions are attached to timers. IBM Cloud Functions supports this out-of-the-box so we don't need to implement timers ourselves.