Remove usage of `auth_` prefix and replace with masm attribute

[partylikeits1983]

As described in the compiler weekly sync call, we need to replace the usage of the auth_ prefix in authentication procedures and replace with a masm attribute.

@bobbinth @bitwalker @greenhat Please let me know if there is something else I need to add to address this issue completely.

[mmagician]

I'd keep the attribute name just auth for simplicity.

[PhilippGackstatter]

I'm in favor of simplicity, but also consistency. Since @note_script is now also a procedure instead of a script (but we're still calling it note script), I think we should consider using @auth_script (and in general call it "auth script" instead of "auth procedure"). This would be consistent with note script and tx script.