Cache control of /package/<pkg>/maintainers/ is incorrect

[bgamari]

Given that this is dynamic and hopefully cheap-to-generate I think we should prohibit the CDN from caching this endpoint. With the status quo one can be very easily confused by adding a new maintainer and then finding that the change is not reflected in the maintainers list.

[sauclovian-g]

There are a lot of such problems, e.g. if you do "delete all candidates" for a package, the old candidates remain on the candidate page indefinitely. And, perhaps most vexingly, if you upload a replacement candidate the candidate display still shows the old one. (This is still true even if you delete it explicitly first.) This makes updating candidates kind of tricky.