refact(credentiallibrary): Switch subtype attributes to oneof

This updates the credential library resources to use a oneof for
attributes. This allows requests to the credential library service to
leverage the new subtypes.AttributeTransformerInterceptor so that
attributes are strongly typed prior to the service handler.

internal/proto/controller/api/resources/credentiallibraries/v1/credential_library.proto

@@ -7,6 +7,7 @@ option go_package = "github.com/hashicorp/boundary/sdk/pbs/controller/api/resour
 import "google/protobuf/timestamp.proto";
 import "google/protobuf/wrappers.proto";
 import "google/protobuf/struct.proto";
+import "google/api/visibility.proto";
 import "controller/api/resources/scopes/v1/scope.proto";
 import "controller/custom_options/v1/options.proto";
 
@@ -16,7 +17,10 @@ message CredentialLibrary {
   string id = 10;
 
   // The ID of the Credential Store of which this Credential Library is a part.
-  string credential_store_id = 20 [json_name = "credential_store_id"];
+  string credential_store_id = 20 [
+    json_name = "credential_store_id",
+    (controller.custom_options.v1.subtype_source_id) = true
+  ];
 
   // Output only. Scope information for this Credential Library.
   resources.scopes.v1.ScopeInfo scope = 30;
@@ -40,8 +44,18 @@ message CredentialLibrary {
   // The Credential Library type.
   string type = 90;
 
-  // The attributes that are applicable for the specific Credential Library type.
-  google.protobuf.Struct attributes = 100 [(custom_options.v1.generate_sdk_option) = true];
+  oneof attrs {
+    // The attributes that are applicable for the specific Credential Library type.
+    google.protobuf.Struct attributes = 100 [
+      (custom_options.v1.generate_sdk_option) = true,
+      (custom_options.v1.subtype) = "default"
+    ];
+    VaultCredentialLibraryAttributes vault_credential_library_attributes = 101 [
+      (google.api.field_visibility).restriction = "INTERNAL",
+      (custom_options.v1.generate_sdk_option) = true,
+      (custom_options.v1.subtype) = "vault"
+    ];
+  }
 
   // Output only. The available actions on this resource for this user.
   repeated string authorized_actions = 300 [json_name = "authorized_actions"];
@@ -63,4 +77,4 @@ message VaultCredentialLibraryAttributes {
 
   // The body of the HTTP request the library sends to vault. When set http_method must be "POST"
   google.protobuf.StringValue http_request_body = 30 [json_name = "http_request_body", (custom_options.v1.generate_sdk_option) = true, (custom_options.v1.mask_mapping) = { this: "attributes.http_request_body" that: "HttpRequestBody" }];
-}
+}

internal/proto/controller/api/services/v1/credential_library_service.proto

@@ -8,6 +8,9 @@ import "protoc-gen-openapiv2/options/annotations.proto";
 import "google/api/annotations.proto";
 import "google/protobuf/field_mask.proto";
 import "controller/api/resources/credentiallibraries/v1/credential_library.proto";
+import "controller/custom_options/v1/options.proto";
+
+option (custom_options.v1.domain) = "credential";
 
 service CredentialLibraryService {
   // GetCredentialLibrary returns a stored Credential Library if present.  The provided request