[pre] Metrics from VMs in the pre-evironment arent scraped

Noticed this while we were tearing down the redis-ratelimiting instance in GKE for #2003 (closed). It turned out that there were no metrics in the dashboards for pre. However, after closer investigation, it turned out that there never have been: https://thanos-query.ops.gitlab.net/graph?g0.expr=redis_instance_info%7Benv%3D%22pre%22%2C%20type%3D%22redis-ratelimiting%22%7D&g0.tab=0&g0.stacked=0&g0.range_input=1y&g0.max_source_resolution=0s&g0.deduplicate=1&g0.partial_response=0&g0.store_matches=%5B%5D&g0.end_input=2022-11-16%2015%3A00%3A04&g0.moment_input=2022-11-16%2015%3A00%3A04

@igorwwwwwwwwwwwwwwwwwwww Noticed that the exporters are correctly running on the vms, but mentioned that there's no prometheus-vm in pre scraping the others:

grepping the port in chef-repo:

$ ag 9121

roles/ops-infra-prometheus-server.json
156:          "exporter_port": "9121",

roles/gstg-infra-prometheus-server.json
437:          "exporter_port": "9121",

roles/ops-infra-gitlab.json
165:          "listen_address": "0.0.0.0:9121"

roles/gprd-infra-prometheus-server.json
1079:          "exporter_port": "9121",

note that pre is missing