add primary/foreign key information in the model level of dbt docs generate

[salimmoulouel]

resolves #10034
resolves dbt-labs/dbt-bigquery#1186
resolves dbt-labs/dbt-docs#507

Problem

Primary/foreign key not included in the dbt docs serve when declared at the model level

Solution

Imprive the code

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
• This PR includes type annotations for new and modified functions

[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.

[dbeatty10]

The only thing I'm seeing changed in this PR is the core/dbt/task/docs/index.html file.

As mentioned here, this file comes from the dbt-docs repository, and is generated by the dbt maintainers when a release is packaged. So this isn't a file we'd expect to see changed directly by an external contributor, and I'm going to close this particular PR.

But if you made some changes to the dbt-docs repo that you want to propose, could you share screenshots in dbt-labs/dbt-docs#507 and we can discuss further?