code: def upgrade():
      op.add_column(
          "experiments",
          sa.Column("creation_time", sa.BigInteger(), nullable=True),
      )
      op.add_column(
          "experiments",
          sa.Column("last_update_time", sa.BigInteger(), nullable=True),
      )
  
imports: from alembic import op
  import sqlalchemy
label_desc: Use image node_id 1 for calling a global function with example usage: upgrade() without return types