chore: Move agent availability to Account level (#3074)

- Move agent availability to the account level

db/schema.rb

@@ -35,6 +35,8 @@ ActiveRecord::Schema.define(version: 2021_09_29_150415) do
     t.datetime "created_at", precision: 6, null: false
     t.datetime "updated_at", precision: 6, null: false
     t.datetime "active_at"
+    t.integer "availability", default: 0, null: false
+    t.boolean "auto_offline", default: true, null: false
     t.index ["account_id", "user_id"], name: "uniq_user_id_per_account_id", unique: true
     t.index ["account_id"], name: "index_account_users_on_account_id"
     t.index ["user_id"], name: "index_account_users_on_user_id"