Icu 5651 create spk type (#1266)

Add functionality for creating a ssh private key credential and add
corresponding acceptance tests.

✅ Closes: ICU-5651

Co-authored-by: Cameron Perera <cameron.perera@hashicorp.com>
Co-authored-by: Randall Morey <randall@randallmorey.com>
Co-authored-by: Zhihe Li <zhihe.li@hashicorp.com>

addons/api/addon/serializers/credential.js

@@ -26,15 +26,19 @@ export default class CredentialSerializer extends ApplicationSerializer {
   serializeUsernamePassword() {
     const serialized = super.serialize(...arguments);
     // Remove non-username_password type attributes
-    delete serialized['attributes']['private_key'];
-    delete serialized['attributes']['passphrase'];
+    delete serialized.attributes.private_key;
+    delete serialized.attributes.passphrase;
     return serialized;
   }
 
   serializeSSHPrivateKey() {
     const serialized = super.serialize(...arguments);
     // Remove non-ssh_private_key type attributes
-    delete serialized['attributes']['password'];
+    delete serialized.attributes.password;
+    if (!serialized?.attributes?.passphrase)
+      delete serialized.attributes.passphrase;
+    if (!serialized?.attributes?.private_key)
+      delete serialized.attributes.private_key;
     return serialized;
   }
 
@@ -42,7 +46,9 @@ export default class CredentialSerializer extends ApplicationSerializer {
     const normalizedHash = copy(hash, true);
     const normalized = super.normalize(typeClass, normalizedHash, ...rest);
     // Remove passphrase as we don't track it after being created/updated
-    delete normalized['data']['attributes']['passphrase'];
+    normalized.data.attributes.passphrase = '';
+    normalized.data.attributes.password = '';
+    normalized.data.attributes.private_key = '';
     return normalized;
   }
 }