enhancement: support consumer custom labels in ApisixConsumer

[kayx23]

Summary

Please triage whether ApisixConsumer should support user-defined consumer labels in addition to the controller-generated labels.

Current behavior

APISIX itself supports consumer labels, but ApisixConsumer does not currently provide a way to define custom labels on the APISIX consumer.

From the current implementation:

• ApisixConsumer does not expose a field for consumer custom labels
• the translator sets consumer.Labels = label.GenLabel(ac)
• label.GenLabel only generates controller metadata labels such as kind, name, namespace, and resource key

As a result, consumer label use cases supported by APISIX cannot currently be expressed through ApisixConsumer.

Use cases affected

• setting business or tenant labels on a consumer
• using those labels in workflows that depend on consumer label metadata, such as attach-consumer-label

Code context

• api/v2/apisixconsumer_types.go
• internal/adc/translator/apisixconsumer.go
• internal/controller/label/label.go