Confirm non-utf8 proto string behavior

[cretz]

Describe the solution you'd like

In Go when we switched from gogoproto to common proto, we recognized that the former allowed invalid utf8 but not the latter. We have seen a potential case where a user may have set invalid utf-8 in a proto Failure message. We need to confirm whether Java proto library even allows this (in either direction if possible, but especially at marshal time), and then assess our options.

[Quinn-With-Two-Ns]

Confirmed the java proto library does not allow non-utf8 proto string