Add 'suppressSend' and 'suppressDisplay' event types to proposition-event-type schema, Add 'reason' to proposition-action schema

## What are the schemas that are affected by the issue
1. [/proposition-event-type.schema.json
](https://github.com/adobe/xdm/blob/master/extensions/adobe/experience/decisioning/proposition-event-type.schema.json) - addition of two new event proposition types: `suppressSend` and `suppressDisplay` for events that have been suppressed during send and display respectively

2. [/proposition-action.schema.json](https://github.com/adobe/xdm/blob/master/extensions/adobe/experience/decisioning/proposition-action.schema.json) - addition of a new property `reason` to indicate why a proposition event has been suppressed

## What are examples of products that are impacted by the issue
Adobe Journey Optimizer (Inbound Delivery Service)

Start by reading proposition-event-type.schema.json and proposition-action.schema.json under extensions/adobe/experience/decisioning. Add the two named event types and the reason property as described; done means both schemas represent suppressed send/display events and explain their suppression reason.

Written by the indexing model from the issue text.