Response Play Responder to Optional and User Email to Case Insensitive

[stmcallister]

The responder field on the pagerduty_response_play resource is, in fact, not required on the PagerDuty API. Correcting the resource schema to match that fact. Response Play test results.

TF_ACC=1 go test -run "TestAccPagerDutyResponsePlay" ./pagerduty -v -timeout 120m
=== RUN   TestAccPagerDutyResponsePlay_import
--- PASS: TestAccPagerDutyResponsePlay_import (7.50s)
=== RUN   TestAccPagerDutyResponsePlay_Basic
--- PASS: TestAccPagerDutyResponsePlay_Basic (9.21s)
PASS
ok  	github.com/terraform-providers/terraform-provider-pagerduty/pagerduty	17.387s

Also set the email field to suppress diff when there is a difference in case, since emails are case insensative.

TF_ACC=1 go test -run "TestAccPagerDutyUser_Basic" ./pagerduty -v -timeout 120m
=== RUN   TestAccPagerDutyUser_Basic
--- PASS: TestAccPagerDutyUser_Basic (7.43s)
PASS
ok  	github.com/terraform-providers/terraform-provider-pagerduty/pagerduty	8.063s