Subscriptions docs could do with some useful examples

### Current State

The subscriptions docs could do with some examples of useful actions. For example:

- [ ] It's not clear that the PUT end point for /subscriptions can be used to patch an existing subscription, an example request exercising this would also be helpful along with some commentary on what fields are overridden
- [ ] A sample of a webhook configuration would be useful
- [ ] Under the webhook retry options it's not clear what format of string should be passed

### Desired State

Docs should show a sample of using the PUT /subscriptions API to make a config change, for example adding retry or updating a filter
Docs should list exactly which fields in the existing subscription are overridden when you use the subscription name to update an existing subscription with a PUT
Docs should contain an example API request to create a webhook subcription
The retry options description should include the time units for the initial and max delays.