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

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

docs/components/data-sources/slack.mdx

@@ -16,7 +16,7 @@ This will automatically retrieve data from the workspace associated with the use
 
 ```python
 import os
-from embedchain import Pipeline as App
+from embedchain import App
 
 os.environ["SLACK_USER_TOKEN"] = "xoxp-xxx"
 app = App()