fix: Standardise kafka (client|writer|tenant-tee) metric names

[benclive]

What this PR does / why we need it:
The metric names are very inconsistent. Some of them are wrapped in loki_distributor and kafka, others are not and don't have any prefix (!)

• kafka_client.WriterClient => Now adds loki_distributor_kafka_ prefix to metrics. These come from a lib and expect a registerer.
• kafka_client.Producer => Now adds loki_distributor_ prefix to metrics. These are our own code so we are already adding the kafka_ prefix but not the other bits.
• tenant_tee => These were manually adding loki_distributor_ which I've wrapped in a registerer. It also containers a Producer client which inheririts the registerer and adds its own kafka_ prefix (as before).

This makes it a bit easier to search for these metrics. Previously they were hard to find, as some of them were called things like buffered_fetch_records which are now loki_distributor_kafka_buffered_fetch_records.

[ashwanthgoli]

this would also add the prefix to the producer metrics, is this intentional? an alternative could be to register with a constant label that says producer="tenant_topic_tee"