Is "android_secret_code" a code to unlock the SIM?
No, android_secret_codes contains a list of dialer codes to enter hidden menus. It is typed in Dialer to enter those hidden menus (they are usually in form of *#-------#).

You need the PUK Code (PIN Unlock Key) to unlock your specific SIM card. You can get PUK from your carrier network. You can call them and get the PUK once you verify your identity.