Move Vault's customized pkcs7 fork into a shared location (#24658)

- The PKI plugin needs to use the customized pkcs7 fork
   so move it out from the aws credential plugin's package
   into a shared location

.copywrite.hcl

@@ -8,7 +8,7 @@ project {
   # Supports doublestar glob patterns for more flexibility in defining which
   # files or folders should be ignored
   header_ignore = [
-    "builtin/credential/aws/pkcs7/**",
+    "helper/pkcs7/**",
     "ui/node_modules/**",
     "enos/modules/k8s_deploy_vault/raft-config.hcl",
     "plugins/database/postgresql/scram/**",

builtin/credential/aws/path_login.go

@@ -26,14 +26,14 @@ import (
 	"github.com/aws/aws-sdk-go/service/iam"
 	"github.com/aws/aws-sdk-go/service/sts"
 	"github.com/hashicorp/errwrap"
-	cleanhttp "github.com/hashicorp/go-cleanhttp"
+	"github.com/hashicorp/go-cleanhttp"
 	"github.com/hashicorp/go-retryablehttp"
 	"github.com/hashicorp/go-secure-stdlib/awsutil"
 	"github.com/hashicorp/go-secure-stdlib/parseutil"
 	"github.com/hashicorp/go-secure-stdlib/strutil"
-	uuid "github.com/hashicorp/go-uuid"
+	"github.com/hashicorp/go-uuid"
 
-	"github.com/hashicorp/vault/builtin/credential/aws/pkcs7"
+	"github.com/hashicorp/vault/helper/pkcs7"
 	"github.com/hashicorp/vault/sdk/framework"
 	"github.com/hashicorp/vault/sdk/helper/cidrutil"
 	"github.com/hashicorp/vault/sdk/helper/jsonutil"