merge exclude columns for incremental models

[dave-connors-3]

resolves #5260

Description

This PR allows a user to specify a list of columns not to update during an incremental run using the merge strategy. This is achieved via a new macro get_merge_update_columns that will take into account user input from either merge_update_columns or the new merge_exclude_columns config to return the correct set of columns to update.

This will need to be dispatched to accomodate slightly different behavior in the dbt-spark repository.

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have signed the CLA
• [x] 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 opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• [x] I have run changie new to create a changelog entry

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[jtcohen6]

Thanks @dave-connors-3! I'm tagging this ready_for_review, and adding it to the review queue for the Adapters team.

In order to merge this PR, we'll want a functional test for merge_exclude_columns that lives in dbt-tests-adapter, and runs successfully when pulled into dbt-snowflake + dbt-bigquery + dbt-spark.

It would make sense for this new test to live alongside the existing tests for merge_update_columns. Currently, those tests live only in each adapter plugin, and not yet converted to use the new pytest framework:

• dbt-snowflake: TestIncrementalMergeColumns
• dbt-bigquery: TestIncrementalMergeColumns
• dbt-spark: TestDeltaStrategies

[dave-connors-3]

hey @jtcohen6! I think we should be good to go on added tests --

Spark BQ Snowflake

I likely missed something, so let me know what else needs to be done!

[kd2718]

Our team would love to have this feature. What is the status of this PR?

[leahwicz]

@nathaniel-may could this be a PR that you prioritize the team to get some eyes on and review please?