chore(web/atom-feed): Move feed generator out of //users/tazjin

I intend to use this for updates on TVL projects, which will end up on
the homepage, which is outside of //users.

Change-Id: I03542d1bcef3d9fc4599294655caab5ed22ba5d9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3728
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

users/tazjin/homepage/feed.nix

@@ -7,7 +7,8 @@ let
   inherit (builtins) map readFile sort foldl';
   inherit (lib) max singleton;
   inherit (pkgs) writeText;
-  inherit (depot.users.tazjin) atom-feed blog renderMarkdown;
+  inherit (depot.web) atom-feed;
+  inherit (depot.users.tazjin) blog renderMarkdown;
 
   postToEntry = defun [ blog.post atom-feed.entry ] (post: rec {
     id = "https://tazj.in/blog/${post.key}";