[daggy-u] [dbt] - Update DU copy in docs (DEV-68) (#20250)

## Summary & Motivation

This PR updates some copy in the docs to more generally describe DU as a
whole, instead of only the Essentials course.

## How I Tested These Changes

👀

docs/content/getting-started/what-why-dagster.mdx

@@ -61,7 +61,7 @@ If you want to try running Dagster yourself, check out the Dagster [Quickstart](
 
 Ready to dive in? Depending on your learning preferences, there are a few ways to get started:
 
-- [Dagster University](https://courses.dagster.io) - An in-depth, step-by-step course with quizzes and practice problems focusing on the essentials of building in Dagster. Completing the course takes from six to 10 hours.
+- [Dagster University](https://courses.dagster.io) - In-depth, step-by-step courses with quizzes and practice problems focusing on building in Dagster.
 - [Tutorial](/tutorial) - Not as lengthy or detailed as Dagster University, the tutorial focuses on building a small data pipeline that retrieves data from HackerNews.
 - [Concepts](/concepts) - Detailed information about Dagster’s core concepts.
 - [Guides](/guides) - Step-by-step guides for completing specific tasks with Dagster.