OptConfig should have a setting "optOutArchivedRepos"

[Hixie]

When we enable allstar on the flutter org, it filed about 37 issues complaining that branch protection wasn't enabled on various repos.

All of these were archived, read-only repos. These don't need branch protection, since they have the ultimate protection of being entirely unmodifiable.

[jeffmendoza]

I haven't looked into the repo metadata GitHub for read-only. I'll take a look. We should probably have something like optOutReadOnly similar to optOutPrivateRepos

[jeffmendoza]

Updated title.
Similar to the #54 optOutPrivateRepos setting. current logic is here:

allstar/pkg/config/config.go

Line 162 in eec32e0

func isEnabled(ctx context.Context, o OrgOptConfig, r RepoOptConfig, rep repositories, owner, repo string) (bool, error) {