feat(mongodb): add support for generated instance name (scaleway#4206)

Author: scaleway-bot

cmd/scw/testdata/test-all-usage-mongodb-instance-create-usage.golden

@@ -7,7 +7,7 @@ USAGE:
 
 ARGS:
   [project-id]                                             Project ID to use. If none is passed the default project ID will be used
-  [name]                                                   Name of the Database Instance
+  [name=<generated>]                                       Name of the Database Instance
   version                                                  Version of the MongoDB™ engine
   [tags.{index}]                                           Tags to apply to the Database Instance
   node-number                                              Number of node to use for the Database Instance