docs: Adding Elastic as a User (argoproj#9636)

Update USERS.md

Adding Elastic as a User to Argo Workflow

Signed-off-by: Christopher Cutajar <60098546+christophercutajar@users.noreply.github.com>

Signed-off-by: Christopher Cutajar <60098546+christophercutajar@users.noreply.github.com>

USERS.md

@@ -69,6 +69,7 @@ Currently, the following organizations are **officially** using Argo Workflows:
 1. [EBSCO Information Services](https://www.ebsco.com/)
 1. [Enso Finance](https://enso.finance/)
 1. [Equinor](https://www.equinor.com/)
+1. [Elastic](https://www.elastic.co/)
 1. [Fairwinds](https://fairwinds.com/)
 1. [FOLIO](http://corp.folio-sec.com/)
 1. [FreeWheel](https://freewheel.com/)