Description of the problem:

UI 2.24.5 - We Allow handling multi-document YAML files in custom manifests page, but no indication for this to the user.
We should add such helper/doc for the user to understand this is an option, instead of uploading 1 manifests at a time 

How reproducible:

100%

Steps to reproduce:

1. Add the multi-document YAML option to the new custom manifest section.

People:

SME: Adrien Gentil
QE: Tal Hilzenrat