Optional support for static Extra Links without XCom dependency

### Description

This feature request entails the addition of an opt-in feature for extra links which are not stored as an XCom, for static URLs and reduced metaDB bloat.

### Use case/motivation

As far as I'm aware, extra links are only supported via XComs. This makes sense for dynamic, task-instance specific / DAG-run specific URLs (e.g. a link to an external Spark job); however, XComs are _not_ an ideal mechanism for static URLs which are only specific to the given operator (rather than the task instance). For example, a very common use case for the Extra Links feature is to point to a static, operator-specific documentation page. Yet, storing that URL in an XCom for each task instance is clearly not ideal in that circumstance, and only adds bloat to the metaDB.

### Related issues

Only very tangentially related: https://github.com/apache/airflow/issues/54527

### Are you willing to submit a PR?

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

Caveat: I am willing to help with the backend implementation, but I have no understanding or experience regarding react / frontend development.

### 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 by tracing Airflow's existing extra-link entry points and how they write and read XComs, then inspect the related React frontend behavior. Done should mean an opt-in path supports static operator-specific URLs without creating per-task XCom entries, with coverage for the backend and frontend behavior.

Written by the indexing model from the issue text.