[Feature] Allow setting of a lookback as top level model property

[QMalcolm]

Housekeeping

• I am a maintainer of dbt-core

Short description

In #10624 we're building a new type of incremental model strategy, microbatch. To support that we need a concept of lookback. The lookback is essentially how far to look back in multiples of the batch_size when automatically setting the event_time_start. So if event_time_end="2024-09-04 13:44:00", batch_size="day", and lookback=4, then the event_start_time would be set to 2024-08-31 00:00:00.
If defining it in the model sql it'd look like

-- my_model.sql
{{ config(
     materialization='incremental',
     incremental_strategy='microbatch',
     event_time='my_time_field',
     batch_size='day',
     lookback=0, -- int, defaults to 0 if not specified
   )
}}
...

If defining it in the model yaml it'd look like:

models:
  - name: my_model
     config:
       event_time: my_time_field
       incremental_strategy: microbatch
       batch_size: day
       lookback: 0 # int, defaults to 0 if not specified

Acceptance criteria

• a lookback value can be specified in a model's config
• the lookback value should default to 0 if not specified
• the lookback value alters the generated event_time_start by a multiple of the batch_size

Suggested Tests

• a lookback value can be specified in a model's config (via yaml and sql)
• the lookback value is default to 0 if not specified
• the lookback value alters the generated event_time_start by a multiple of the batch_size

Impact to Other Teams

Cloud artifacts, new property in the config of models

Will backports be required?

No

Context

No response

[QMalcolm]

Resolved by #10594