Track all workers concurrency

Prerequisite to using AIMD to dynamically set concurrency limit: gitlab-com/gl-infra/observability/team#3815 (comment 2188997620)

Since we will be using Concurrency Limit for throttling jobs, we have to track all workers concurrency. Currently only workers with concurrency_limit (eg) defined attribute is tracked.

Note that tracking all workers/jobs would add substantial amount of requests to ServiceRedisClusterQueuesMeta, so we will gradually rollout the feature flag gitlab-org/gitlab#527022 (closed) carefully to ensure we don't saturate on the Redis Cluster

Edited by Marco Gregorius
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