Links broken in `Templates` doc

### What do you see as an issue?

https://airflow.apache.org/docs/apache-airflow/stable/templates-ref.html
The links for objects such as `DagRun` / `DAG` / `TaskInstance` / `BaseOperator` appear no longer functional - which makes it quite difficult to tell what you can actually get from those objects while accessing them via jinja templates (or via `Context`)

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

Start with the Templates reference page at https://airflow.apache.org/docs/apache-airflow/stable/templates-ref.html and inspect the links for DagRun, DAG, TaskInstance, and BaseOperator. Confirm the relevant object documentation is reachable for users working with Jinja templates or Context, then verify that all affected links resolve correctly.

Written by the indexing model from the issue text.