Merge branch 'uploads-csp-changes' into 'develop'

Uploads: Sandbox them in the CSP.

See merge request pleroma/pleroma!2389

lib/pleroma/plugs/uploaded_media.ex

@@ -41,6 +41,7 @@ def call(%{request_path: <<"/", @path, "/", file::binary>>} = conn, opts) do
         conn ->
           conn
       end
+      |> merge_resp_headers([{"content-security-policy", "sandbox"}])
 
     config = Pleroma.Config.get(Pleroma.Upload)