Enable render_as_batch=True for alchemy migrations
Enable render_as_batch=True for alchemy migrations

This is needed to effect non-trivial migrations on sqlite (it can only
migrate column names; not change column types). This setting is safe for
other DB servers (like postgres or mysql) since alembic will opt to use
those server's native capabilities.

lsst-sqre/ltd-keeper,lsst-sqre/ltd-keeper