Add metadata to Monitor::APM pages

Bringing these into the Monitor fold thanks to the PM identifying
them.

doc/development/distributed_tracing.md

+---
+stage: Monitor
+group: APM
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Distributed Tracing - development guidelines
 
 GitLab is instrumented for distributed tracing.

doc/development/elasticsearch.md

+---
+stage: Monitor
+group: APM
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Elasticsearch knowledge **(STARTER ONLY)**
 
 This area is to maintain a compendium of useful information when working with Elasticsearch.

doc/development/instrumentation.md

+---
+stage: Monitor
+group: APM
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Instrumenting Ruby code
 
 [GitLab Performance Monitoring](../administration/monitoring/performance/index.md) allows instrumenting of both methods and custom

doc/development/logging.md

+---
+stage: Monitor
+group: APM
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # GitLab Developers Guide to Logging
 
 [GitLab Logs](../administration/logs.md) play a critical role for both

doc/development/prometheus.md

+---
+stage: Monitor
+group: APM
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Working with Prometheus
 
 For more information on working with [Prometheus metrics](prometheus_metrics.md), see

doc/development/prometheus_metrics.md

+---
+stage: Monitor
+group: APM
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
 # Working with Prometheus Metrics
 
 ## Adding to the library