Don't render overridden sources twice in docs site

[drewbanin]

Describe the feature

If a project overrides a source declared in a package, the docs site will render the source twice in the DAG view (and probably the file tree, too). Let's update the docs site to reflect the logical source constructed by dbt.

@beckjake can you advise what changes, if any, should take place in the compiled manifest? I'd be relatively happy with some JS logic in the docs site to merge sources together, but the more work dbt can do here, the better! Any chance we can have sources indicating which other sources they override, or which sources override them?

[beckjake]

I've thought about this a bit in the context of ref, and doc too. When we are parsing, we collect docrefs, refs, and sources - but only the literal arguments received. During compilation, we could either change those values (seems bad) or add new fields indicating the UIDs that were actually selected.

We almost do this with the depends_on value, but it only includes nodes. Maybe we could extend that to sources and docs as well?

[drewbanin]

The code change here appears to be pretty minimal - AFAICT from testing out #2357 in dev, it looks like we just need to point to manifest.sources instead of manifest.nodes in some places.

[drewbanin]

fix is here: dbt-labs/dbt-docs#87

Going to smoke test this change some more, then PR the index.html file in dbt