Prepare release (#651)

# Description
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## Checklist
(For exoscale contributors)

* [x] Changelog updated (under *Unreleased* block)
* [ ] Testing

## Testing

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CHANGELOG.md

@@ -1,10 +1,10 @@
 # Changelog
 
-## Unreleased
+## 1.81.0
 
 ### Features
 
-- Private Network: support for DHCP options (dns-server/ntp-server/router/domain-search)
+- Private Network: support for DHCP options (dns-server/ntp-server/router/domain-search) #644
 
 ### Improvements