Alerts (notifications) when components reach certain milestones

[liskin]

I'd like a way to get notified when a chain/casette/tyre is near its expected lifetime.
This could be implemented as a third report type (--report=alerts).

Open question is the configuration UX: do we declare this per-component?

components:
  chain11-1:
    name: Shimano CN-HG700-11
    alert-kms: 3000

or do we want generic per-bike/role alerts?

alerts:
  gravel:
    chain:
      kms: 3000
  road:
    chain:
      kms: 4000

or both?

Feedback welcome.