inability to remember metrics

#### Overview of the Issue

Issue https://github.com/hashicorp/consul/issues/5140 was closed, on the basis that https://github.com/hashicorp/consul/pull/9198 addresses it.

Except, the issue https://github.com/hashicorp/consul/issues/5140 mentions two problems:
1. Only changed metrics are initialized on Consul start
(Which is addressed by https://github.com/hashicorp/consul/pull/9198)
2. After `prometheus_retention_time` expires they also get removed
(Which is not addressed.)

The change https://github.com/hashicorp/consul/pull/9198 will initialize metrics at startup, only to forget them once `prometheus_retention_time` expires.

Start by reading issue #5140 and PR #9198, then trace the Go code handling prometheus_retention_time and metric lifecycle. Confirm the existing startup initialization behavior and identify where expiration removes metrics. Done means a regression test demonstrates the intended metric retention behavior after the retention period.

Written by the indexing model from the issue text.