Remerge of hashtag following (#341)

this time with less idiot

Co-authored-by: FloatingGhost <hannah@coffee-and-dreams.uk>
Reviewed-on: https://akkoma.dev/AkkomaGang/akkoma/pulls/341
Signed-off-by: mkljczk <git@mkljczk.pl>

priv/repo/migrations/20221203232118_add_user_follows_hashtag.exs

@@ -0,0 +1,12 @@
+defmodule Pleroma.Repo.Migrations.AddUserFollowsHashtag do
+  use Ecto.Migration
+
+  def change do
+    create table(:user_follows_hashtag) do
+      add(:hashtag_id, references(:hashtags))
+      add(:user_id, references(:users, type: :uuid, on_delete: :delete_all))
+    end
+
+    create(unique_index(:user_follows_hashtag, [:user_id, :hashtag_id]))
+  end
+end