Respect value set for full_refresh in config

[grindheim]

Describe the bug

Attempts to disable full-refresh for an incremental model, either by setting +full_refresh: false in dbt_project.yml or full_refresh = false in a model's config, is ignored when running dbt run --full-refresh.

Steps To Reproduce

Create a new, incremental model with the following definition:

{{ config(
    materialized = 'incremental',
    full_refresh = false
    ) 
}}
select CURRENT_TIMESTAMP() AS ChangeTimestamp

Then run dbt run --select <model_name> --full-refresh twice.

Finally, run a select query against the table that selects the min and max value for the change timestamp.

select min(ChangeTimestamp), max(ChangeTimestamp) from <database_name>.<model_name>

This will give the same value for both the min and the max timestamp.

Expected behavior

The full-refresh config setting should be respected when the FULL_REFRESH flag is used, meaning that an incremental table with the config full_refresh = false should always load incrementally except for the first time the model is run.

The error is caused by line 13 in incremental.sql:
https://github.com/dbt-labs/dbt-spark/blob/main/dbt/include/spark/macros/materializations/incremental/incremental.sql
{%- set full_refresh_mode = (flags.FULL_REFRESH == True) -%}

This does not respect the config definition, and does instead solely rely on the FULL_REFRESH flag.

The correct definition for this is as defined in dbt-core/dbt-snowflake/etc
https://github.com/dbt-labs/dbt-core/blob/v0.21.1rc1/core/dbt/include/global_project/macros/materializations/incremental/incremental.sql

{%- set full_refresh_mode = (should_full_refresh()) -%}

This has been tested locally and shown to work as expected.

Screenshots and log output

System information

The output of dbt --version:

installed version: 0.21.0
   latest version: 0.21.0

Up to date!

Plugins:
  - snowflake: 0.21.0
  - bigquery: 0.21.0
  - redshift: 0.21.0
  - spark: 0.21.0
  - postgres: 0.21.0

NB: the plugin that is used is dbt-spark.

The operating system you're using:
Distributor ID: Debian
Description: Debian GNU/Linux 11 (bullseye)
Release: 11
Codename: bullseye

The output of python --version:
Python 3.8.12

Additional context

Add any other context about the problem here.

[jtcohen6]

@grindheim Thanks for the issue and the PR!