Backport of Update telemetry.mdx RPC Metrics into release/1.12.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #19593 to be assessed for backporting due to the inclusion of the label backport/1.12.

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The below text is copied from the body of the original PR.

---

Update Server Workload telemetry section to demonstrate explicitly enabling metric emission as they're default disabled.

Description

Customers need to be aware that if investigating server workload via metrics this needs to be explicitly enabled.

Testing & Reproduction steps

• Run any support version of Consul or Consul Enterprise
• Enable telemetry in agent config viaprometheus_retention_time
• Observe default blocked prefixes showing consul.rpc.server.call:

$ consul agent -dev -node localhost -client 127.0.0.1 -hcl 'telemetry { prometheus_retention_time = "10m" }'

$ curl -s localhost:8500/v1/agent/self | jq -r '.DebugConfig.Telemetry.BlockedPrefixes'                                                                                                                                                                                          
[
  "consul.rpc.server.call"
]

• Enable RPC metrics using telemetry.prefix_filter and observe permission and emission of desired metrics:

$ consul agent -dev -node localhost -client 127.0.0.1 -hcl 'telemetry { prometheus_retention_time = "10m" prefix_filter = [ "+consul.rpc.server.call" ]}'

$ curl -s localhost:8500/v1/agent/self | jq -r '.DebugConfig.Telemetry.AllowedPrefixes'                                                                                                                                                                                  
[
  "consul.rpc.server.call"
]

Links

• Consul Telemetry Agent Config Default Prefix Filter default disabling.

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• ea11497 - 8df9c6f - e2a3294

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[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR

[natemollica-nm]

Closed as this backport was to an unsupported version