dbaas: x/api new commands (#631)

# Description
`exo api` bump for enabling usage of the new DBaaS external endpoints
and integrations feature.
See: exoscale/dbaas-api#286
[Draft External Integrations
Guide](https://github.com/exoscale/dbaas-api/blob/master/doc/integrations/external_integrations_guide.md)

## Checklist
(For exoscale contributors)

* [x] Changelog updated
* [x] Testing - tested with local build

## Testing

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Describe the tests you did
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CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- DBaaS: external endpoints and integrations commands #631
+
 ### Improvements
 
 - go.mk: update to v2.0.2 #630