Handle Product Notifications

Changes

Added NotifyProduct event that is emitted by the Monitor when a product notification needs to be sent.
- The Monitor is in charge of providing the product, the webhooks that should be notified, and the type of notification that should go through
Added WebhookManager class to memoize discord clients (Slack will be added in the future).
- This also translates data from the single product object to parameters that work for the discord webhook builder.
- Each time a NotifyProduct event is triggered webhooks are sent.
Updated Manager to receive a data Store object (from @monitor/datastore). This will allow persistant data to be updated and queried.
- Proxy data is pull each time a new monitor process starts to register new proxies
- Product data is updated each time a NotifyProduct event is triggered