[Feature] ERD in dbt docs

### Is this your first time submitting a feature request?

- [x] I have read the [expectations for open source contributors](https://docs.getdbt.com/docs/contributing/oss-expectations)
- [x] I have searched the existing issues, and I could not find an existing issue for this feature
- [x] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

### Describe the feature

I want to be able to see the ERD in dbt docs.
DBT can create relationships in the database, but does not show it in the docs when its generated.

### Describe alternatives you've considered

_No response_

### Who will this benefit?

_No response_

### Are you interested in contributing this feature?

_No response_

### Anything else?

_No response_

No files or tests are named. Start by examining the dbt-docs entry points and how generated documentation currently represents database relationships; done means the generated docs display an ERD for those relationships.

Written by the indexing model from the issue text.