Allow nais apps to access (read: get access through secrets) by referencing aiven resource name

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Ref: https://nav-it.slack.com/archives/C9P60F4F3/p1753178182008279?thread_ts=1753167596.542789&cid=C9P60F4F3

1. Don't require users to understand two different naming schemes to get naiserator to correctly wire up secrets
2. Improve/update documentation