Doc:Rename internal collection to legacy collection

Fixes #11858

Author: karenzone

docs/static/monitoring/monitoring-internal-legacy.asciidoc

@@ -1,13 +1,13 @@
 [role="xpack"]
 [[monitoring-internal-collection-legacy]]
-=== Collect {ls} monitoring data using internal collectors
+=== Collect {ls} monitoring data using legacy collectors
 ++++
-<titleabbrev>Internal collection</titleabbrev>
+<titleabbrev>Legacy collection</titleabbrev>
 ++++
 
-==== Components for internal collection
+==== Components for legacy collection
 
-Monitoring {ls} with internal collection uses these components:
+Monitoring {ls} with legacy collection uses these components:
 
 * <<logstash-monitoring-collectors-legacy,Collectors>>
 * <<logstash-monitoring-output-legacy,Output>>
@@ -37,9 +37,9 @@ include::monitoring-output-legacy.asciidoc[]
 
 
 [[configure-internal-collectors-legacy]]
-==== Configure {ls} monitoring with internal collectors
+==== Configure {ls} monitoring with legacy collectors
 ++++
-<titleabbrev>Configure internal collection</titleabbrev>
+<titleabbrev>Configure legacy collection</titleabbrev>
 ++++
 
 To monitor Logstash nodes:

docs/static/monitoring/monitoring-overview.asciidoc

@@ -21,8 +21,8 @@ monitoring data from your {ls} instance and sends it directly to your monitoring
 cluster. The benefit of Metricbeat collection is that the monitoring
 agent remains active even if the {ls} instance does not.
 
-* <<monitoring-internal-collection-legacy,Internal collection>>. 
-Internal collectors send monitoring data to your production cluster.
+* <<monitoring-internal-collection-legacy,Legacy collection>>. 
+Legacy collectors send monitoring data to your production cluster.
 
 include::monitoring-mb.asciidoc[]
 include::monitoring-internal-legacy.asciidoc[]

docs/static/settings/monitoring-settings-legacy.asciidoc

@@ -1,6 +1,6 @@
 [role="xpack"]
 [[monitoring-settings-legacy]]
-==== Monitoring settings for internal collection
+==== Monitoring settings for legacy collection
 ++++
 <titleabbrev>Monitoring Settings</titleabbrev>
 ++++