Don't omit 'inputs' field in pagerduty_incident_workflow as it's required by the API

[tganderson0]

Currently, the client omits fields that are empty when serializing to JSON. However, the API endpoint https://api.pagerduty.com/incident_workflows/id, which is used for updating Incident Workflows, requires that the field inputs exists in the payload. This makes it so that you cannot use the create zoom room action (or any others that do not have an input) without a 'fake' input.

This also addresses the issue in PagerDuty/terraform-provider-pagerduty#840

API Response without the inputs defined

import requests

url = "https://api.pagerduty.com/incident_workflows/id"

payload = { "incident_workflow": {
        "name": "Example Incident Workflow",
        "description": "This Incident Workflow is an example",
        "steps": [
            {
                "name": "Send Status Update",
                "action_configuration": {
                    "action_id": "pagerduty.com:incident-workflows:send-status-update:1",
                }
            }
        ]
    } }
headers = {
    "Accept": "application/json",
    "Content-Type": "application/json",
    "Authorization": "Token token=---------"
}

response = requests.put(url, json=payload, headers=headers)

print(response.json())

> {'message': 'Invalid body: "incident_workflow.steps[0].action_configuration.inputs" is required'}

This is copied from my PR in the terraform provider which uses this client- PagerDuty/terraform-provider-pagerduty#992.

[imjaroiswebdev]

@tganderson0 thank you very much for finding and patching this. 🏆