Add support for dbt config-blocks

[romeo-alexander]

As far as I can tell, when it comes to model configs (eg. tags, pre/post hooks, materialization, enablement/disablement) in dbt-ibs, we can only specify them in either the dbt_project.yml project file, or a properties.yml file. Having dbt-ibs support the specification of these configs directly in the .ibis file, so that they are precompiled as a jinja dbt config block, would be very useful.

For example, it would be good to have the flexibility to specify configs in the following way:

@config(
    {
        "enabled": True if get_flags().target == "batch" else False,
    }
)
def model(table):
    return table

or

@config(
    {
        "materialized": "table" if get_flags().target == "batch" else "view",
    }
)
def model(table):
    return table

The idea is that the vast majority of the query logic applies to the multiple database contexts I may want to manager (specifically, batch and streaming), but to handle the parts that are different (eg. materialization, handling "now()"), being able to switch contexts directly in a config decorator would prevent having to maintain entirely separate dbt projects for each database context.