Feature/incremental predicates

[dave-connors-3]

resolves dbt-core issue #3923 for snowflake users

Description

This PR enables users to supply arbitrary filters on their incremental models to reduce the table scan resources when using Snowflake.

-- sample config

{{
    config(
        incremental_strategy='merge',
        materialized='incremental',
        unique_key = 'cc_call_center_sk',
        incremental_predicates = [{
            "source_col":"cc_call_center_id",
            "expression":"like 'AAA%'"
        },
        {
            "source_col":"cc_call_center_id",
            "expression":"not like 'BBB%'"
        }]
   

Log output:

23:05:58.503176 [debug] [Thread-1  ]: On model.staging_party.sample_callcenter: merge into analytics.dbt_dconnors.sample_callcenter as DBT_INTERNAL_DEST
        using analytics.dbt_dconnors.sample_callcenter__dbt_tmp as DBT_INTERNAL_SOURCE
        on 
    DBT_INTERNAL_SOURCE.cc_call_center_sk = DBT_INTERNAL_DEST.cc_call_center_sk
    and DBT_INTERNAL_DEST.cc_call_center_id like 'AAA%' and DBT_INTERNAL_DEST.cc_call_center_id not like 'BBB%' 

TODO before merge:
[ ] Merge dbt-core PR#4546

Checklist

• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt-snowflake next" section.

[VersusFacit]

Oh, hi there, the™️ @dave-connors-3 👋

Love the contribution, and I kind of want to resuscitate this at a leisurely pace, since it seems there's some sizable work already in the hopper here.

• Mind updating the Readme to link to the relevant issue? I had trouble locating it myself. I wonder if it was closed 🤔 found it hiding in Core!
• a changelog entry (one sentence) would be nice too!
• any additional context outside the original issue that's needed before trying to merge these through?

Get those things there, and I can see about reviewing this.

Edit: Dave and I chatted it up. They'll be leisurely keeping up on this. Just wanted to log that's its still in the works at least round this time

[dave-connors-3]

hey @VersusFacit ! i think we can close this PR, and take it up after The Great Materialization Refactor work currently going on