feat: As a user I want to be able to create consumer groups declaratively

[bpasson]

Description

As a user I want to be able to create consumer groups declaratively so I can specify plugin configurations for those groups. Right now e.g. I cannot define a limit-count restriction on a consumer group declaratively. I have to create it using the api or attach them directly to the route, which makes it hard if routes belong to multiple consumer groups.

[github-actions]

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