As per Gorkem:

It is for vscode-yaml the yaml extension for vscode. We are
planning to publish this on vscode marketplace [2]. Similar to what we had done
for vscode-java [3].
It needs a 128x128 image that roughly represents yaml. I do not think there is a
real figure that represents yaml so something that includes word yaml in it?

[1] https://github.com/redhat-developer/vscode-yaml
[2] https://marketplace.visualstudio.com/
[3] https://marketplace.visualstudio.com/items?itemName=redhat.java