Change account ids to snowflake ids (#15844)

Co-authored-by: Eugen Rochko <eugen@zeonfederated.com>

db/migrate/20210306164523_account_ids_to_timestamp_ids.rb

+class AccountIdsToTimestampIds < ActiveRecord::Migration[5.1]
+  def up
+    # Set up the accounts.id column to use our timestamp-based IDs.
+    safety_assured do
+      execute("ALTER TABLE accounts ALTER COLUMN id SET DEFAULT timestamp_id('accounts')")
+    end
+
+    # Make sure we have a sequence to use.
+    Mastodon::Snowflake.ensure_id_sequences_exist
+  end
+
+  def down
+    execute("LOCK accounts")
+    execute("SELECT setval('accounts_id_seq', (SELECT MAX(id) FROM accounts))")
+    execute("ALTER TABLE accounts ALTER COLUMN id SET DEFAULT nextval('accounts_id_seq')")
+  end
+end

db/schema.rb

@@ -142,7 +142,7 @@ ActiveRecord::Schema.define(version: 2021_03_24_171613) do
     t.index ["target_account_id"], name: "index_account_warnings_on_target_account_id"
   end
 
-  create_table "accounts", force: :cascade do |t|
+  create_table "accounts", id: :bigint, default: -> { "timestamp_id('statuses'::text)" }, force: :cascade do |t|
     t.string "username", default: "", null: false
     t.string "domain"
     t.string "secret", default: "", null: false