Consumer group name cannot be overridden in block-builder and live-store #7897

Describe the bug
In Tempo 3.0 microservices mode (Kafka ingest path), the consumer group names used by the block-builder, live-store, and metrics-generator components cannot be prefixed or customised. This makes Tempo unusable on shared/multi-tenant Kafka clusters

Observed consumer group names (Tempo v3.0.3):
Component │ Consumer group (on the wire)
block-builder │ block-builder
live-store │ tempo-distributed-live-store
metrics-generator │ metrics-generator

None of these can be given a tenant prefix (e.g., mytenant.block-builder).

The CLI flag -ingest.consumer-group exists (-help-all) and can be set, but the block-builder ignores it. Verified on the wire: with -ingest.consumer-group=mytenant.block-builder set on the container, the FindCoordinator request still uses group=block-builder.
Same outcome for live-store (-ingest.consumer-group ignored; group stays tempo-distributed-live-store) and metrics-generator (-generator.consumer-group ignored; group stays metrics-generator).

There is an open PR which fixes it for metrics-generator. #7613

To Reproduce
Steps to reproduce the behavior:

1. Deploy tempo-distributed (chart 3.5.1, appVersion Tempo 3.0.3) in microservices mode.
2. Set -ingest.consumer-group=mytenant.block-builder on the block-builder and live-store (and -generator.consumer-group=mytenant.metrics-generator on metrics-generator).
3. Observe via Kafka broker logs / a protocol-aware proxy that the FindCoordinator/OffsetFetch requests still use groups block-builder, tempo-distributed-live-store, metrics-generator — the override has no effect.
4. On a Kafka cluster with a PREFIXED/tenant-prefix consumer-group ACL, consumption fails with GROUP_AUTHORIZATION_FAILED error.

Expected behavior
Allow the consumer group name for each Kafka-consuming component to be configurable, e.g.:

• Honor -ingest.consumer-group / ingest.kafka.consumer_group for block-builder and live-store, and -generator.consumer-group for metrics-generator; or
• Add a global ingest.kafka.consumer_group_prefix that is prepended to all internally-derived group names.
  Ideally the derived name would still keep per-component distinctness (e.g., .block-builder, .live-store, .metrics-generator) so the components remain separate consumer groups.

Environment:

• Infrastructure: EKS 1.36
• Deployment tool: Helm
• Tempo version: v3.0.3 (chart grafana-community/tempo-distributed 3.5.1).