Include an endpoint to serve alerting systems

[ljoss17]

Summary

Hermes sometimes detects events which should be acted upon, these might be logged as warning but can be easily missed.

Problem Definition

Here are two potential use cases for this:

1. When a chain upgrades and increments the version, e.g. chainname-1 to chainname-2, the Hermes configuration needs to be updated and the relayer needs to be restarted. Since chains emit an event upon upgrade https://github.com/cosmos/ibc-go/issues/270 Hermes could send a notification in this situation.
2. Hermes could notify when it detects a client which will expire soon.

Proposal

Introducing an endpoint to serve alerting systems, such as https://github.com/prometheus/alertmanager, could allow operators to setup a notification system to avoid missing some important information.

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