chore: remove unused container-azm-ms-osmconfig ConfigMap

[zanejohnson-azure]

What

Removes kubernetes/container-azm-ms-osmconfig.yaml — the sample ConfigMap used to enable Open Service Mesh (OSM) Prometheus scraping by ama-logs.

Why

OSM scraping support in ama-logs is effectively unused. Telemetry from the last 30 days:

Metric	Count
Clusters with container-azm-ms-osmconfig ConfigMap applied	33
Clusters actually scraping OSM metrics (osmNamespaceCount > 0)	0

Query used (against the Container Insights agent App Insights):

customMetrics
| where timestamp > ago(30d)
| where name == "NodeCoreCapacity"
| where isnotempty(tostring(customDimensions.osmNamespaceCount))
| extend ClusterArmId = tostring(customDimensions.ID),
         osmNs        = toint(customDimensions.osmNamespaceCount)
| summarize UniqueClusters      = dcount(ClusterArmId),
            ClustersScrapingOSM = dcountif(ClusterArmId, osmNs > 0)

Every cluster that has the ConfigMap mounted has monitor_namespaces empty — no one is actually using the feature. Additionally, OSM was archived by CNCF in early 2024.

Scope

This PR only removes the sample ConfigMap manifest as a first deprecation step. The agent code paths that read it are left in place for now and can be removed in a follow-up:

• build/linux/installer/scripts/tomlparser-osm-config.rb
• OSM blocks in source/plugins/ruby/in_kube_nodes.rb and source/plugins/go/src/telemetry.go
• $AZMON_TELEGRAF_OSM_PROM_PLUGINS placeholders in build/linux/installer/conf/telegraf-*.conf
• Helm chart volume mounts for container-azm-ms-osmconfig in charts/azuremonitor-containers*/templates/
• Documentation/OSMPrivatePreview/

Risk

Low — this file is a sample manifest. Removing it doesn't affect any cluster where it has already been applied (the ConfigMap continues to exist on those clusters until explicitly deleted). It just stops shipping the template in the repo.