[OCPBUGS-1631]: Replace AWS STS svg with png

Author: jeana-redhat

authentication/managing_cloud_provider_credentials/cco-mode-sts.adoc

@@ -23,7 +23,7 @@ Requests for new and refreshed credentials are automated by using an appropriate
 //to-do: more detailed info on this flow
 
 .STS authentication flow
-image::142_OpenShift_credentials_STS_0221.svg[Detailed authentication flow between AWS and the cluster when using AWS STS]
+image::142_OpenShift_credentials_STS_0221.png[Detailed authentication flow between AWS and the cluster when using AWS STS]
 //to-do: improve alt-text
 
 Using manual mode with STS changes the content of the AWS credentials that are provided to individual {product-title} components.