Phase 1:

• Update googleanalytics-alpha config to use the name "_ga" for origin cookie while keeping AMP_ECID_GOOGLE for non-origin cases (based on using Allow variation of Client ID based on display context #8847)

Phase 2:

• Update googleanalytics config to use the name "_ga" for origin cookie while keeping AMP_ECID_GOOGLE for non-origin cases (based on using Allow variation of Client ID based on display context #8847)
• Update ads to use "_ga" on origin and "AMP_ECID_GOOGLE" for non-origin