Don't create temp tables at plan time unless they're actually needed

[georgesittas]

We currently create temporary tables at plan time preemptively, even though they may not necessarily be needed. This behavior was introduced before we started to create tables on demand (i.e., if they're missing), but we can move away from it now.

For instance, the initial plan application for the example project produces the following tables in duckdb:

CREATE TABLE sqlmesh__sqlmesh_example.sqlmesh_example__full_model__3031530868(item_id INTEGER, num_orders BIGINT);
CREATE TABLE sqlmesh__sqlmesh_example.sqlmesh_example__full_model__3031530868__temp(item_id INTEGER, num_orders BIGINT);
CREATE TABLE sqlmesh__sqlmesh_example.sqlmesh_example__incremental_model__141311533(id INTEGER, item_id INTEGER, event_date DATE);
CREATE TABLE sqlmesh__sqlmesh_example.sqlmesh_example__incremental_model__141311533__temp(id INTEGER, item_id INTEGER, event_date DATE);
CREATE TABLE sqlmesh__sqlmesh_example.sqlmesh_example__seed_model__1248844913(id INTEGER, item_id INTEGER, event_date DATE);
CREATE TABLE sqlmesh__sqlmesh_example.sqlmesh_example__seed_model__1248844913__temp(id INTEGER, item_id INTEGER, event_date DATE);

[erindru]

This would also help with having less tables for the janitor to clean up.

Recent changes have made the actual snapshot deployability available in the strategy create() method (previously, only a doctored DeployabilityIndex was available that always returned "not deployable").

So we could use this to skip creating the dev preview ("__temp") tables if the snapshot being created is deployable