Add changeset for Service Account provider fix

Author: polRk

.changeset/fix-service-account-key-cleaning.md

@@ -0,0 +1,10 @@
+---
+'@ydbjs/auth-yandex-cloud': patch
+---
+
+Fix Service Account provider: clean private key in constructor
+
+- Move private key cleaning from JWT creation to constructor for better performance
+- Remove unnecessary log about warning line detection
+- Add key ID to debug logs for better traceability
+- Directly modify key.private_key instead of creating new object