Add support for Incident Custom Fields and sanitize Orchestration PUT request

[swbradshaw]

This PR adds support for Incident Custom Fields on the Event Orchestration path. This feature will be released in January 2024. In addition it fixes the API call for updating the Event Orchestration.

Changes:

• Added new EventOrchestrationPathIncidentCustomFieldUpdate struct which is an ID/Value pair of the custom field
• Added this new property to existing EventOrchestrationPathRuleActions struct
• Updated test in pagerduty/event_orchestration_path_test.go for new action type
• In the process of testing Getting/Saving a Service Orchestration, I determined there was a bug in this client where it was sending null values for arrays. This is not allowed by the API and results in an HTTP 400 Bad Request. I've added functions sanitizeOrchestrationPath and sanitizeActions to replace null values with empty arrays.

The following is a test client I wrote to test this library. The code below simply gets the service orchestration and then updates it with the same object from the get request. Without the sanitize change, this library throws an error.

func main() {
	client, err := pagerduty.NewClient(&pagerduty.Config{
		Token: os.Getenv("PAGERDUTY_TOKEN")})
	if err != nil {
		panic(err)
	}

	servicesResp, _, err := client.Services.List(&pagerduty.ListServicesOptions{})
	if err != nil {
		panic(err)
	}
	serviceId := servicesResp.Services[0].ID
	
	servicePathResp, _, err := client.EventOrchestrationPaths.Get(serviceId, "service")
	if err != nil {
		panic(err)
	}
	
	updatePayload, _, err := client.EventOrchestrationPaths.Update(serviceId, "service", servicePathResp)
	if err != nil {
		panic(err)
	}

}

[imjaroiswebdev]

Thank you for adding this very needed fix @swbradshaw, however before moving on, there are a few comments which need to be addressed to continue with the merge. So, please if You find We need to discuss this further don't hesitate in reaching me out. ✌🏽

[imjaroiswebdev]

LGTM! 👍🏽