Feature/update freshness config

[fivetran-jamie]

PR Overview

Package version introduced in this PR:
v0.12.0

This PR addresses the following Issue/Feature(s):

fivetran/dbt_ad_reporting#148

Summary of changes:

Updates freshness to align with the new config framework introduced in dbt Core v1.9. Documents how users on older versions of dbt Core will/can interface with freshness

Submission Checklist

• Alignment meeting with the reviewer (if needed)
  • Timeline and validation requirements discussed
• Provide validation details:
  • Validation Steps: Check for unintentional effects (e.g., add/run consistency & integrity tests)

older versions of dbt do not run freshness tests, but there's no error message

• Testing Instructions: Confirm the change addresses the issue(s)

dbt v1.9 prior to our update: freshness tests run but there's a deprecation message for some folks (idk why I am not getting it despite being on dbt v1.9.8?)

dbt v1.9 with our update: successfully runs freshness without any deprecation notice

• Focus Areas: Complex logic or queries that need extra attention

Changelog

• Draft changelog for PR
• Final changelog for release review

[fivetran-joemarkiewicz]

LGTM