DAG fails to render if operation (on-run-* hook) has parents

[jtcohen6]

Describe the bug

If an operation (on-run-* project hook) depends on a model, it creates an entry for that operation in parent_map + child_map in manifest.json, which throws off the DAG rendering logic. It is possible to still use the DAG viz by adding --select criteria, i.e. by filtering out the operation node.

It's arguable whether operations should be included in parent_map + child_map, but isn't strictly wrong that they are. Changing that would require an artifact schema change. For now, it feels appropriate to handle this in the dbt-docs DAG rendering logic.

Steps To Reproduce

# dbt_project.yml
on-run-end:
  - "{{ reference_my_model() }}"

-- macros/reference_my_model.sql
{% macro reference_my_model() %}

    select 1 from {{ ref('my_model') }}

{% endmacro %}

-- models/my_model.sql
select 1 as id

$ dbt docs generate
$ dbt docs serve

I haven't been able to successfully run npm on this machine, so I can't generate source maps and get a more helpful pointer to a specific line of code. That's definitely the thing to do first.

The output of dbt --version:
This fails in v1.0.1 and v0.21.1, so at least this isn't a regression in v1.0. But it's pretty obnoxious, and I bet the fix is straightforward, so I'd like to include in dbt-core==1.0.2 if we can.

[jtcohen6]

It's possible my theory for the cause of this bug is incomplete—folks are seeing it even without on-run-end hooks, or on-run-end hooks that reference other resources. See slack threads for more details