feat(types): add accountId to the credential identity interface (#1240)

* feat(identity): add accountId to the credential identity interface

* chore(types): add changeset

* chore(types): update docstring for accountId

Author: siddsriv

.changeset/strong-timers-join.md

@@ -0,0 +1,5 @@
+---
+"@smithy/types": minor
+---
+
+adds accountId to the AwsCredentialIdentity interface

packages/types/src/identity/awsCredentialIdentity.ts

@@ -24,6 +24,11 @@ export interface AwsCredentialIdentity extends Identity {
    * AWS credential scope for this set of credentials.
    */
   readonly credentialScope?: string;
+
+  /**
+   * AWS accountId.
+   */
+  readonly accountId?: string;
 }
 
 /**