345b0c560a
Serve static plugin assets with a `Cache-Control: no-cache, public` header. This avoids caching a 404 response for such an asset, preventing it from being loaded until expiry even if the file later becomes available. This is currently preventing updates of plugins on community and would generally affect any customer with a cache in front of the Mattermost servers. Fixes: https://mattermost.atlassian.net/browse/MM-20948