Add ARN-based resource identity to SSMContacts

[its2shar]

Description

Add resource identity to ARN-based resources in SSMContacts. This includes:

• aws_ssmcontacts_contact_channel

Relations

Relates #42983
Relates #42984

Output from Acceptance Testing

TF_ACC=1 go test -v ./internal/service/ssmcontacts -run TestAccSSMContacts_serial/ContactChannelResource/identity -timeout 30m
2025/09/24 15:56:25 Creating Terraform AWS Provider (SDKv2-style)...
2025/09/24 15:56:25 Initializing Terraform AWS Provider (SDKv2-style)...
=== RUN   TestAccSSMContacts_serial
=== PAUSE TestAccSSMContacts_serial
=== CONT  TestAccSSMContacts_serial
=== RUN   TestAccSSMContacts_serial/ContactChannelResource
=== RUN   TestAccSSMContacts_serial/ContactChannelResource/identity_Basic
=== RUN   TestAccSSMContacts_serial/ContactChannelResource/identity_ExistingResource
--- PASS: TestAccSSMContacts_serial (104.02s)
    --- PASS: TestAccSSMContacts_serial/ContactChannelResource (104.02s)
        --- PASS: TestAccSSMContacts_serial/ContactChannelResource/identity_Basic (44.88s)
        --- PASS: TestAccSSMContacts_serial/ContactChannelResource/identity_ExistingResource (59.15s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/ssmcontacts        109.981s

[github-actions]

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[anurag-hashicorp]

We need to create a changelog:
.changelog/<pr-number>.txt

[jar-b]

This doesn't match the base config from the standard tests. It creates a replication set resource, e.g.

func testAccContactChannelConfig_base() string {
	return fmt.Sprintf(`
resource "aws_ssmincidents_replication_set" "test" {
  region {
    name = %[1]q
  }
}
`, acctest.Region())
}

This discrepancy is causing the acceptance tests to fail.

=== RUN   TestAccSSMContacts_serial/ContactChannelResource/identity_ExistingResource
    contact_channel_identity_gen_test.go:125: Step 1/2 error: Error running pre-apply plan: exit status 1

        Error: reading SSMIncidents Replication Set: empty result

          with data.aws_ssmincidents_replication_set.test,
          on main_gen.tf line 24, in data "aws_ssmincidents_replication_set" "test":
          24: data "aws_ssmincidents_replication_set" "test" {}

[jar-b]

Lets remove the _ here for consistency with other test names.

Suggested change

	"identity_Basic": testAccSSMContactsContactChannel_Identity_Basic,
	"identity_ExistingResource": testAccSSMContactsContactChannel_Identity_ExistingResource,
	"identityBasic": testAccSSMContactsContactChannel_Identity_Basic,
	"identityExistingResource": testAccSSMContactsContactChannel_Identity_ExistingResource,

[jar-b]

Exclude the tags template for any resources which are not the primary subject of the test case.

Suggested change

{{- template "tags" . }}