Configure SMTP relay for Google Cloud

Hello all new to the forum. I tried searching for and did not see any results so posting this here.

I have gitlab (14.7.3) running in GCP (google cloud platform) and wanting to use the with my google workspace account.

I see there is a setting called gitlab_rails['smtp_authentication'] = "login" setting; however, I do not need to login (as the sender account does not exist I am using the IP address to authorize). What other options to this setting exist? Also where are each of these setting documented (I see examples; however, no alternatives to each key.

Also, is there a way to set the HELO or EHLO strings on the SMTP connect string?