logger: added ref to run-time logging levels after removing NVLOG. (#578)

Signed-off-by: Christoph Pakulski <paker8848@gmail.com>

docs/root/intro/version_history.rst

@@ -7,6 +7,8 @@ Version history
   <arch_overview_load_balancing_types_round_robin>` support. The round robin
   scheduler now respects endpoint weights and also has improved fidelity across
   picks.
+* logger: all :ref:`logging levels <operations_admin_interface_logging>` can be configured
+  at run-time: trace debug info warning error critical.
 
 1.6.0
 =====

docs/root/operations/admin.rst

@@ -127,6 +127,8 @@ modify different aspects of the server:
 
   See :option:`--hot-restart-version`.
 
+.. _operations_admin_interface_logging:
+
 .. http:get:: /logging
 
   Enable/disable different logging levels on different subcomponents. Generally only used during