x/build/app/appengine: builders with non-zero KnownIssue are not grayed out in the golang.org/x repo sections

[bcmills]

The openbsd-mips64-jsing builder is greyed out on the dashboard for the main repo, and for the x/net repo in isolation.

However, its entry is not greyed out for the x/net repo in the golang.org/x/ repos summary section, where it shows as a red failure.

CC @golang/osp-team

[dmitshur]

The feature of graying out a builder with a known issue has been implemented in x/build/app/appengine but only for the main section. It should be grayed out in the golang.org/x repository sections as well, that work hasn't been done yet. It's a matter of modifying the templates and data passed to incorporate this additional axis of information.

This can be fixed directly in x/build/app/appengine (sooner, but duplicate work), or wait for #34744 to be completed where this work has already been started.