Feature/enable null urls

[fivetran-catfritz]

Are you a current Fivetran customer?

Fivetran created PR.
What change(s) does this PR introduce?

• For use in the dbt_ad_reporting package, users can now allow records having nulls in url fields to be included in the ad_reporting__url_report model.
• Disabled the not_null test for linkedin_ads__url_report when null urls are allowed

Did you update the CHANGELOG?

• Yes

Does this PR introduce a breaking change?

• Yes (please provide breaking change details below.)
• No (please provide an explanation as to how the change is non-breaking below.)

Did you update the dbt_project.yml files with the version upgrade (please leverage standard semantic versioning)? (In both your main project and integration_tests)

• Yes

Is this PR in response to a previously created Bug or Feature Request

• Yes, Issue/Feature #59
• No

How did you test the PR changes?

• BuildKite
• Local (please provide additional testing details below)

Select which warehouse(s) were used to test the PR

• BigQuery
• Redshift
• Snowflake
• Postgres
• Databricks
• Other (provide details below)

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