Add config for conditional update on incremental merge strategy

[fbalmigere]

Hello,

We're facing an issue where we would like to make use of the feature (in snowflake at least), to add some condition in the "when matched" statement, in order to not actually update on match, if none of the relevant values columns have actually been modified. But it seems not to be available with incremental strategy.

    {% if unique_key %}
    when matched then update set
        {% for column_name in update_columns -%}
            {{ column_name }} = DBT_INTERNAL_SOURCE.{{ column_name }}
            {%- if not loop.last %}, {%- endif %}
        {%- endfor %}
    {% endif %}

Suggestion pseudocode:
merge on xyz
when matched [and {check if any of the column from a list have actually changed} ]
then update set [...]

I'm surprised this isn't already in the default config, given that use case shouldn't be too rare.

Am I missing something here?