start oban app in migrations and mix tasks

lib/mix/pleroma.ex

@@ -13,7 +13,8 @@ defmodule Mix.Pleroma do
     :flake_id,
     :swoosh,
     :timex,
-    :fast_html
+    :fast_html,
+    :oban
   ]
   @cachex_children ["object", "user", "scrubber", "web_resp"]
   @doc "Common functions to be reused in mix tasks"

priv/repo/migrations/20200825061316_move_activity_expirations_to_oban.exs

@@ -6,6 +6,8 @@ defmodule Pleroma.Repo.Migrations.MoveActivityExpirationsToOban do
   def change do
     Pleroma.Config.Oban.warn()
 
+    Application.ensure_all_started(:oban)
+
     Supervisor.start_link([{Oban, Pleroma.Config.get(Oban)}],
       strategy: :one_for_one,
       name: Pleroma.Supervisor

priv/repo/migrations/20200907092050_move_tokens_expiration_into_oban.exs

@@ -6,6 +6,8 @@ defmodule Pleroma.Repo.Migrations.MoveTokensExpirationIntoOban do
   def change do
     Pleroma.Config.Oban.warn()
 
+    Application.ensure_all_started(:oban)
+
     Supervisor.start_link([{Oban, Pleroma.Config.get(Oban)}],
       strategy: :one_for_one,
       name: Pleroma.Supervisor