It is not part of adhan or Iqama.
This is the fatwa of His Eminence in the (Islamic Laws):
"Ruling 905. The sentence (أَشْهَدُ أَنَّ عَلِیّاً وَّلِيُّ اللهِ) (ashhadu anna ʿaliyyaw waliyyul lāh) is not a part of adhān and iqāmah, but it is good to say it after the sentence ‘ashhadu anna muḥammadar rasūlul lāh’ with the intention of attaining proximity to Allah."