Disable the release files button until all files have attempted to upload the max number of times

[rebkwok]

Now that files upload asynchronously, a request might stay in Approved status for a while, until all the files have uploaded. Previously this only happened if a file upload errored.

Currently the frontend behaviour will be the same as it was before if a file upload errored (except that it doesn't say the release failed) - the status will be approved, and the release files button will still be enabled. Clicking it again will re-release the files (in the sense that it'll make another audit event and update the released-at date), but it won't affect the actual uploading that's in progress). We want to wait until files have all finished attempting to upload before letting the user try to re-release.