Replace examples of x-mdx with new top level documentation field.

[wcrum]

As title states, in v0.68.1 Zarf released the ability to package Zarf documentation within the zarf.yaml.

Across the examples, we should remove x-mdx for documentation.

Success Criteria:

1. The zarf.dev website renders x-mdx
   https://docs.zarf.dev/ref/examples/argocd/

[AustinAbro321]

Great idea, I hope this increases the usage of the documentation field!