Merge branch 'docs-usage-ping-changes-default-on' into 'master'

Docs: Usage ping changes should be default on

See merge request gitlab-org/gitlab!44501

doc/development/telemetry/usage_ping.md

@@ -444,6 +444,8 @@ Recommendations:
   metric's name and week of the year, `2020-33-{metric_name}`.
 - Use a [feature flag](../../operations/feature_flags.md) to have a control over the impact when
   adding new metrics. 
+- Feature flags should be [default on](../documentation/feature_flags.md#criteria)
+  before final release to ensure we receive data from self-managed instances.
 
 ##### Known events in usage data payload