Adding custom_headers to delivery_method in webhook_subscription resource

[devops-rob]

This PR adds the ability to configure custom headers in the webhook_subscription resource.

[stmcallister]

Thanks for the PR @devops-rob!! I think this will be a great feature for the provider. However, when I run the test for the Webhook Subscription resource I get the following error. Could you address that? Thanks!

TF_ACC=1 go test -run "TestAccPagerDutyWebhookSubscription" ./pagerduty -v -timeout 120m  
=== RUN   TestAccPagerDutyWebhookSubscription_import
panic: interface conversion: interface {} is map[string]interface {}, not map[string]string

goroutine 392 [running]:
github.com/terraform-providers/terraform-provider-pagerduty/pagerduty.expandDeliveryMethod(...)
	.../terraform-provider-pagerduty/pagerduty/resource_pagerduty_webhook_subscription.go:203
github.com/terraform-providers/terraform-provider-pagerduty/pagerduty.buildWebhookSubscriptionStruct(0xc0000ee070)
	 .../terraform-provider-pagerduty/pagerduty/resource_pagerduty_webhook_subscription.go:105 +0x616
github.com/terraform-providers/terraform-provider-pagerduty/pagerduty.resourcePagerDutyWebhookSubscriptionCreate(0xc0002ede00, {0x19b86a0, 0xc0000ee070})
	 .../terraform-provider-pagerduty/pagerduty/resource_pagerduty_webhook_subscription.go:115 +0x58
....

[smaeda-ks]

@stmcallister 🤝

FYI, @devops-rob My PR to the underlying PD client library just got merged: heimweh/go-pagerduty#81
so I may propose you to just run go mod vendor, and try my earlier attempt here:
smaeda-ks@127f634

That should work, but there's one caveat that I mentioned in that PR above:
heimweh/go-pagerduty#81 (comment)

[devops-rob]

Thanks @stmcallister and @smaeda-ks. The tests are now passing my end. Let me know what you see on your side if anything isn't working

[smaeda-ks]

@devops-rob Can you also update the dependency to advance the commit hash?
https://github.com/PagerDuty/terraform-provider-pagerduty/blob/master/go.mod#L8

$ go get github.com/heimweh/go-pagerduty@41d374b4d21bb32712d9a2a5db2bf0f232d4cc53
$ go mod vendor

That will update go.mod (as well as go.sum) in this repo and sync /vendor directory, which is necessary when using the new client library version. This may include other unrelated client library changes but as long as it can be compiled and tests are passing it should be fine. Files under /vendor directory are usually managed by the go mod command and should be untouched manually.

[smaeda-ks]

@devops-rob Thanks for updating this PR! I've left one last comment (suggestion) but otherwise this looks good to me :)

[stmcallister]

Thanks for the combined effort on this everyone! And, sorry for the delay on me getting back to this. Any chance one of you could resolve the conflicts? Thanks!

[stmcallister]

@devops-rob would you be able to fix the conflicts in this PR?

[devops-rob]

Hey @stmcallister Sorry for the delay. The notification got lost in my jungle of an inbox. I've resolved all the conflicts now so should be good to go. Thanks for all you help on this @smaeda-ks too

[stmcallister]

Hey @devops-rob! Thanks for fixing the conflicts! While giving this one more look I noticed you're naming the field custom_headers in the schema. I also know that you (HashiCorp) recommend that we use plural names as items in a list as a best practice. However, in an effort to keep naming conventions consistent in the PagerDuty provider we ask that these fields be listed as singular. A good example of this is in the Schedule resource where we have the layer field to represent each layer in a schedule. Will you change the field to be the singular customer_header in the schema?

[devops-rob]

Thanks @stmcallister I've updated the schema as per your comments. Acceptance tests for this resource are passing. Some tests are failing but not related to any resources I have worked on.

[stmcallister]

I added the custom_header field to the acceptance tests and found a few issues 😅 . I've addressed those, add my commit, and will merge this to master. Thanks for adding this! 🎉 👍