Add Global search initial indexing queue size to sidekiq overview

This is a new metric that was introduced in gitlab-org/gitlab!33384 (merged) where more sidekiq Elasticsearch workloads were moved over to using a custom queue mechanism. This chart is exactly the same as the "Global search incremental indexing queue length" one adjecent to it in this dashboard except it is a different queue that is only responsible for newly created projects or newly indexed projects where the other one is tracking incremental updates to already indexed projects.

I did consider adding this line to the existing chart but it seems like there is no good way to do that given the charts both collect an identical metrics from every rails node scraped by Prometheus meaning that there are already many identical lines being displayed in each graph. If we had both in the same graph it would be very difficult to filter to just one of them or visually distinguish them with all the noise. We did discuss aggregation approaches in !2046 (comment 311794699) but still did not land on anything due to there being no way to know which is the most up to date data point for the queue size so instead we display all the lines from every node.

Snapshot