Updating miscellaneous Google example DAGs to use XComArgs

[josh-fell]

Related to #10285

• Updated example DAG files such that xcom_pull() calls use an operator's .output property
• Added comments to which task dependencies, if any, are handled and/or created via XComArgs for transparency
• Removed or refactored the default_args pattern where necessary as requested by @ashb (i.e. removed a separated default_args declaration for deference for declaration as part of the DAG object)
• Other miscellaneous updates based on .output refactoring

Note: There are several instances where the xcom_pull() call was not updated. These instances involve accessing a specific value within the XCom or calling user-defined macros with an XCom value. Reference #16618 for an open issue to enhance the XComArg functionality to provide similar behavior as the classic xcom_pull() method.

Note: Not all DAGs were tested functionally (i.e. with hard integrations to source systems and executed), however each DAG was tested to compile and generate a DAG graph as expected locally.

An detailed summary of all changes made as part of this PR can be found below:

DAG File	Converted xcom_pull()?	Other Updates?	Comments
airflow/providers/google/leveldb/example_dags/example_leveldb.py	No	Yes	Removed unneeded default_args pattern.
airflow/providers/google/marketing_platform/example_dags/example_campaign_manager.py	No	No	Current XComArg object does not support accessing specific values of an iterable XCom value elegantly. Did not update any occurrences in this DAG.
airflow/providers/google/marketing_platform/example_dags/example_display_video.py	Yes **	Yes	** Current XComArg object does not support accessing specific values of an iterable XCom value elegantly. Did not update the following occurrence: '{{ task_instance.xcom_pull("create_sdf_download_task")["name"] }}' All other xcom_pull() calls have been updated. Removed explicit task dependencies that are created via XComArgs. Updated this instance to reference the correct task rather than an non-existant one: '{{ task_instance.xcom_pull("upload_sdf_to_bigquery")}}'
airflow/providers/google/marketing_platform/example_dags/example_search_ads.py	Yes	Yes	Removed explicit task dependencies that are created via XComArgs.
airflow/providers/google/suite/example_dags/example_gcs_to_sheets.py	No	No	Current XComArg object does not support accessing specific values of an iterable XCom value elegantly. Did not update any occurrences in this DAG.
airflow/providers/google/suite/example_dags/example_sheets.py	Yes **	No	** Current XComArg object does not support accessing specific values of an iterable XCom value elegantly. Did not update the following occurrences: "{{ task_instance.xcom_pull('upload_sheet_to_gcs')[0] }}" All other xcom_pull() calls have been updated.

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[josh-fell]

Hi @turbaszek! Just wondering if you've had any time to take a look at this PR and/or if you have any feedback?