Add more, customizable, events

[NoahSaso]

Right now, it only sends messages on proposal creation.

We probably also want to notify when it passes or fails. This may be difficult since proposals can expire without an event, and the indexer only sends webhooks on events. A solution to this may be the indexer sending a webhook when a vote is cast that switches the proposal to pass or fail, and for all proposals that pass or fail upon expiration, maybe Cloudflare Workers let us schedule an event to fire in the future (which we can schedule upon proposal creation based on its expiration time).

The events being sent should be configurable.