Consolidate source + remove combo tests for linkedin

[fivetran-data-model-bot]

Summary

This PR is to combine the source and transform packages and remove tests not compatible with dbt Fusion 1.10.6+.

Please check the below automated updates were successful:

Source + Transform Consolidation

• Merged dbt_linkedin_source into this transformation package.
• Moved models/macros to models/staging/ and macros/staging/.
• Updated all var('') references to use ref('stg_linkedin__').
• Removed the source package from packages.yml.
• Updated vars in dbt_project.yml from refs to sources.
• Major version bump to v1.0.0

dbt Fusion Compatibility

• Removed dbt_utils.unique_combination_of_columns test
• Accepted values tests were removed where applicable (Shopify, NetSuite, QuickBooks).

YAML & Config Updates

• Moved loaded_at_field under config: in src.yml, grouped with freshness
• Added +schema and +materialization for the staging models in dbt_project.yml.

README

• Removed references to the source package in:
  • Overview
  • Installation instructions
  • Dependencies list
  • Schema override examples