Eliminate the NodeRelation class in favor of reusing DeferRelation

[peterallenwebb]

resolves #7823

Problem

Changes the name of a field expected by MetricFlow from schema_name to schema in order to keep plumbing as simple as possible.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[heysweet]

I pinged the others in Cloud Artifacts, but just wanted to call out that @thisispvb and I are working on Explorer, embedded on Cloud Artifacts. We're more than happy to help out here, but just wanted to make sure you knew that we were more disconnected from ingestion and Discovery API serving itself

[jtcohen6]

@peterallenwebb Should we close this PR, since we decided against implementing it and living with the inconsistency (given high cost & lesser benefit)? #7823 (comment)