Ampprojectbot should consider the .protoascii and .out files owned by people working on the validator

[powdercloud]

For the validator, we sync changes developed in Google's internal repo up into Github (we also sync the other direction sometimes, but that's not affected here). This is such a change:
#8134

Ampprojectbot assignes the .protoascii (validator specification files) and .out files (validator test files) to owners of the extensions. This means that getting such a sync requires many approvals, likely slowing down our process.

The solution is probably to patternmatch the protoascii and html and out files for the validator so that we can commit them even if they're in some extension directory. Thanks much for considering.

[powdercloud]

Sorry about the noise - I moved this to the appropriate repo:
google/github-owners-bot#23