fix: enable multikey snapshots

[hoesler]

This PR fixes #615 by adding dynamic column filtering for multiple unique keys

[axellpadilla]

Thanks, closing because the current master version and (v1.9.1) of:

dbt/include/sqlserver/macros/materializations/snapshots/snapshot.sql

already contains the multi-key exclusion logic:

{% set remove_columns = ['dbt_change_type', 'DBT_CHANGE_TYPE', 'dbt_unique_key', 'DBT_UNIQUE_KEY'] %}

{% if unique_key | is_list %}
{% for key in strategy.unique_key %}
{{ remove_columns.append('dbt_unique_key_' + loop.index|string) }}
{{ remove_columns.append('DBT_UNIQUE_KEY_' + loop.index|string) }}
{% endfor %}
{% endif %}

{% set missing_columns = adapter.get_missing_columns(staging_table, target_relation)
| rejectattr('name', 'in', remove_columns)
| list %}

{% set source_columns = adapter.get_columns_in_relation(staging_table)
| rejectattr('name', 'in', remove_columns)
| list %}