[Refactor] Converge Pipeline and App classes (#1021)

Co-authored-by: Deven Patel <deven298@yahoo.com>

docs/use-cases/question-answering.mdx

@@ -24,7 +24,7 @@ Quickly create a RAG pipeline to answer queries about the [Next.JS Framework](ht
 First, let's create your RAG pipeline. Open your Python environment and enter:
 
 ```python Create pipeline
-from embedchain import Pipeline as App
+from embedchain import App
 app = App()
 ```
 

docs/use-cases/semantic-search.mdx

@@ -19,7 +19,7 @@ Embedchain offers a simple yet customizable `search()` API that you can use for
 First, let's create your RAG pipeline. Open your Python environment and enter:
 
 ```python Create pipeline
-from embedchain import Pipeline as App
+from embedchain import App
 app = App()
 ```