Exclude specific entity versions from combine_column_version macro

[bgarf]

Description & motivation

Add the capability to exclude unwanted versions from the combine_column_version macro.

We've encountered a need for this as we have introduced breaking changes to entity versions that cause BigQuery compilation errors when coalescing. For example, a change in field type across versions. This change allows for the avoidance of this by dropping known problematic versions out of the coalesce.

This change makes the assumption that the column's version is always provided as the last 5 characters at the end of the column name (column_X_X_X).

Example of use

To exclude version 1_0_0 from the coalescing:

{%- set all_fields = snowplow_utils.combine_column_versions(
                                relation=ref('snowplow_web_base_events_this_run'),
                                column_prefix='product_v',
                                exclude_versions=['1_0_1'],
                                ) -%}

select
{% for field in all_fields %}
  {{field}} {%- if not loop.last %},{% endif %}
{% endfor %}

# Renders to:
select
  coalesce(product_1_0_2[safe_offset(0)].name, product_1_0_0[safe_offset(0)].name) as name,
  coalesce(product_1_0_2[safe_offset(0)].id, product_1_0_0[safe_offset(0)].id) as id,
  coalesce(product_1_0_2[safe_offset(0)].specs) as specs,
  coalesce(product_1_0_2[safe_offset(0)].specs.power_rating) as specs_power_rating,
  coalesce(product_1_0_2[safe_offset(0)].specs.volume) as specs_volume

Checklist

• [x] I have verified that these changes work locally
• [x] I have updated the README.md (if applicable)
• [ ] I have added tests & descriptions to my models (and macros if applicable)

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[bgarf]

Signed the CLA 👍

[paulboocock]

Bots gone walkies. I can confirm the CLA has been signed.