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

[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 an batch_size. The batch_size is essentially how "big" the incrementing of the model is. It should support the values day, month, and year. The effect in practice is that if your batch_size is day then when the event_start_time is generated in #10636, we can properly calculate what the "start" of a batch should be. Additionally, the lookback which is introduced in #10662 will essentially offset the event_start_time by an integer multiple of the batch_size

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', -- supported values: day, month, year
   )
}}
...

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 # supported values: day, month, year

Acceptance criteria

• batch_size can be set as day, month, or year for an incremental microbatch model

Suggested Tests

• the batch size makes it into the python representation of the model

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