Configuring a single model within `dbt_project.yml`

### Contributions

- [X] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

https://docs.getdbt.com/reference/model-configs#configuring-models and/or https://docs.getdbt.com/reference/source-configs#configuring-sources

### What part(s) of the page would you like to see updated?

### Problem

Many people don't know how to drill all the way down to a single model/source within `dbt_project.yml`.

### Proposed solution

[Sources](https://docs.getdbt.com/reference/source-configs#configuring-sources) has this explainer:

https://github.com/dbt-labs/dbt-core/issues/7128#issuecomment-1936428724 reminds me that we should have something similar on the [models](https://docs.getdbt.com/reference/model-configs#configuring-models) page.

In particular, the config within `dbt_project.yml` for models is not intuitive for everyone:

```yaml
models:
**your_project_name**:
subdirectory_1_name:
subdirectory_2_name:
**model_name**:
+config_name: config_value
```

Sources are ever-so-slightly different:
```yaml
sources:
**your_project_name**:
subdirectory_1_name:
subdirectory_2_name:
**source_name**:
**source_table_name**:
+config_name: config_value
```

### Additional information

There might be other [resource types](https://github.com/dbt-labs/docs.getdbt.com/issues/4314) that this applies to as well.

Start with the linked model-configs and source-configs sections on docs.getdbt.com, then compare the existing source configuration explainer with the proposed dbt_project.yml examples. Done means the documentation clearly shows how to configure one model and one source table, with any additional resource types scoped explicitly.

Written by the indexing model from the issue text.