Clarify how names in topic handler yaml relate to tick script properties and kapacitor.conf settings

This line: https://github.com/influxdata/kapacitor/blob/0e529079ad8384f69e6559622a0d8f9e061097da/alert/DESIGN.md#L82 seems to indicate that the `options` for a topic alert handler of `kind: pagerDuty` map to what you'd use in a tick script, that:

```
id: my_handler
kind: pagerDuty
options:
serviceKey: XXX
```

would be the same as:

```
alert()
.pagerDuty()
.serviceKey('XXX')
```

But [these docs](https://docs.influxdata.com/kapacitor/v1.5/event_handlers/pagerduty/v1/) indicate that `kind` should be `pagerduty` (not `pagerDuty`), and the option name should be `service-key` (not `serviceKey`). These names seem to correlate with the `kapacitor.conf` settings names.

What are the correct names for PagerDuty specifically? And what's the general rule for handler file kind and option names across all alerts?

Start with alert/DESIGN.md#L82 and the linked PagerDuty event-handler documentation, then compare their naming with the kapacitor.conf settings. Clarify the correct PagerDuty kind and option names and document the general naming rule for all alert handlers in the relevant documentation.

Written by the indexing model from the issue text.