feat(hmac-auth) enforce unique consumer

[mideuger]

Summary

There is currently no check regarding the consumer if multiple authentications plugins are used with the AND method. This PR aims to implement this check. It currently is only implemented on hmac-auth plugin as an example.

Full changelog

• Add enforce_unique_consumer flag to plugin configuration
• Check consumer uniqueness when the flag is set
• Add tests showing succeeded and failed authentications using the flag

Issue reference

Fix #8541