add documentation to management collector

src/plugins/kibana_usage_collection/README.md

@@ -6,6 +6,6 @@ This plugin registers the basic usage collectors from Kibana:
 - UI Metrics
 - Ops stats
 - Number of Saved Objects per type
-- Non-default UI Settings
+- [User-changed UI Settings](./server/collectors/management/README.md)
 - CSP configuration
 - Core Metrics

src/plugins/kibana_usage_collection/server/collectors/management/README.md

@@ -0,0 +1,26 @@
+# User-changed UI Settings - Management Collector
+
+The Usage Collector `stack_management` reports user changed settings.
+All user changed UI Settings are automatically collected.
+
+If the configured UI setting might contain user sensitive information simply add the property `sensitive: true` to the ui setting registration config.
+
+```
+uiSettings.register({
+  [NEWS_FEED_URL_SETTING]: {
+    name: i18n.translate('xpack.securitySolution.uiSettings.newsFeedUrl', {
+      defaultMessage: 'News feed URL',
+    }),
+    value: NEWS_FEED_URL_SETTING_DEFAULT,
+    sensitive: true,
+    description: i18n.translate('xpack.securitySolution.uiSettings.newsFeedUrlDescription', {
+      defaultMessage: '<p>News feed content will be retrieved from this URL</p>',
+    }),
+    category: [APP_ID],
+    requiresPageReload: true,
+    schema: schema.string(),
+  },
+}),
+```
+
+The value of any UI setting marked as `sensitive` will be reported as a boolean `true` instead of the actual value. This hides the actual sensitive information while giving us some intelligence over which fields the users are interactive with the most.

src/plugins/kibana_usage_collection/server/collectors/management/types.ts

@@ -89,7 +89,6 @@ export interface UsageStats {
   'sort:options': string;
   'savedObjects:listingLimit': number;
   'query:queryString:options': string;
-  pageNavigation: string;
   'metrics:max_buckets': number;
   'query:allowLeadingWildcards': boolean;
   metaFields: string[];