Test docs generate catalog includes external nodes if available in 1.6.latest

[MichelleArk]

Housekeeping

• I am a maintainer of dbt-core

Short description

External nodes should be included in the catalog as a result of dbt docs generate. This is functional in 1.6.latest but is missing a test.

Acceptance criteria

Add a test that ensures external nodes are included in the catalog from docs generate, if they are available in the manifest.

Suggested Tests

Add a test that ensures external nodes are included in the catalog from docs generate, if they are available in the manifest.

Impact to Other Teams

n/a

Will backports be required?

This should be done on 1.6.latest (effectively a backport) because the test files have differed significantly + this has regressed in 1.7 and would cause conflicts to backport directly.

Context

#9458