Add TTL example to docsite

[danielvegamyhre]

What would you like to be added:
Add TTL example as a task in the docsite: https://github.com/kubernetes-sigs/jobset/blob/main/site/content/en/docs/tasks/_index.md

Why is this needed:
We should have an example in the docsite for every major JobSet feature.

[googs1025]

/assign