Fix service_integration documentation

[viasnake]

Fix service_integration documentation.

body_mode, from_email_mode, and subject_mode of the Email filters can specified with the no-match option.
However, the documentation states that only always and match can be specified.

terraform-provider-pagerduty/pagerduty/resource_pagerduty_service_integration.go

Lines 277 to 311 in 4741e41

	"subject_mode": {
	Type: schema.TypeString,
	Optional: true,
	ValidateDiagFunc: validateValueDiagFunc([]string{
	"always",
	"match",
	"no-match",
	}),
	},
	"subject_regex": {
	Type: schema.TypeString,
	Optional: true,
	},
	"body_mode": {
	Type: schema.TypeString,
	Optional: true,
	ValidateDiagFunc: validateValueDiagFunc([]string{
	"always",
	"match",
	"no-match",
	}),
	},
	"body_regex": {
	Type: schema.TypeString,
	Optional: true,
	},
	"from_email_mode": {
	Type: schema.TypeString,
	Optional: true,
	ValidateDiagFunc: validateValueDiagFunc([]string{
	"always",
	"match",
	"no-match",
	}),
	},