fix(influxdb3): add retention_period to CreateDatabaseRequest (#6629)

Add the undocumented retention_period parameter to the database
creation API for InfluxDB 3 Core.

closes #6610

api-docs/influxdb3/core/v3/ref.yml

@@ -2115,6 +2115,12 @@ components:
       properties:
         db:
           type: string
+        retention_period:
+          type: string
+          description: |
+            The retention period for the database. Specifies how long data should be retained.
+            Use duration format (for example, "1d", "1h", "30m", "7d").
+          example: 7d
       required:
         - db
     CreateTableRequest: