Conditional View Processing / Etag / Modified-Since headers

**Is your feature request related to a problem? Please describe.**
Every upload I have done to the local storage is being retransfered on every page refresh.

**Describe the solution you'd like**
I would like to see an implementation of Conditional View Processing, HTTP Etag or Modified-Since Headers. Especially since the uploads within label-studio won't ever change again, setting an Expires header in 2037 will likely solve the issue as well.

**Describe alternatives you've considered**
I am at this moment considering to instruct a proxy to add these headers.