Add an example of adding/removing a tiering policy for caggs

[zilder]

Description

We extended the add_tiering_policy() / remove_tiering_policy() functions onto continuous aggregate

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[iroussos]

All yours @billy-the-fish to merge or send it back if you don't like something

This is a small update that introduces our newest ability for Tiered Storage: To directly tier continuous aggregates using the standard interface we use for hypertables as well.

[iroussos]

Thank you @billy-the-fish, suggestions look great! Applied all of them - back to you :-)