Set better Cache-Control header for static content

Closes #1382

lib/pleroma/web/endpoint.ex

@@ -12,7 +12,7 @@ defmodule Pleroma.Web.Endpoint do
   plug(Pleroma.Plugs.HTTPSecurityPlug)
   plug(Pleroma.Plugs.UploadedMedia)
 
-  @static_cache_control "public, no-cache"
+  @static_cache_control "public max-age=86400 must-revalidate"
 
   # InstanceStatic needs to be before Plug.Static to be able to override shipped-static files
   # If you're adding new paths to `only:` you'll need to configure them in InstanceStatic as well

test/plugs/cache_control_test.exs

@@ -9,7 +9,7 @@ defmodule Pleroma.Web.CacheControlTest do
   test "Verify Cache-Control header on static assets", %{conn: conn} do
     conn = get(conn, "/index.html")
 
-    assert Conn.get_resp_header(conn, "cache-control") == ["public, no-cache"]
+    assert Conn.get_resp_header(conn, "cache-control") == ["public max-age=86400 must-revalidate"]
   end
 
   test "Verify Cache-Control header on the API", %{conn: conn} do