Add 'since' info (#4316)

Author: andreyaksenov

doc/reference/configuration/configuration_reference.rst

@@ -1243,6 +1243,8 @@ The ``failover`` section defines parameters related to a :ref:`supervised failov
 
 ..  confval:: failover.call_timeout
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A call timeout (in seconds) for monitoring and failover requests to an instance.
 
     | Type: number
@@ -1253,6 +1255,8 @@ The ``failover`` section defines parameters related to a :ref:`supervised failov
 
 ..  confval:: failover.connect_timeout
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A connection timeout (in seconds) for monitoring and failover requests to an instance.
 
     | Type: number
@@ -1263,6 +1267,8 @@ The ``failover`` section defines parameters related to a :ref:`supervised failov
 
 ..  confval:: failover.lease_interval
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A time interval (in seconds) that specifies how long an instance should be a leader without renew requests from a coordinator.
     When this interval expires, the leader switches to read-only mode.
     This action is performed by the instance itself and works even if there is no connectivity between the instance and the coordinator.
@@ -1275,6 +1281,8 @@ The ``failover`` section defines parameters related to a :ref:`supervised failov
 
 ..  confval:: failover.probe_interval
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A time interval (in seconds) that specifies how often a monitoring service of the failover coordinator polls an instance for its status.
 
     | Type: number
@@ -1285,6 +1293,8 @@ The ``failover`` section defines parameters related to a :ref:`supervised failov
 
 ..  confval:: failover.renew_interval
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A time interval (in seconds) that specifies how often a failover coordinator sends read-write deadline renewals.
 
     | Type: number
@@ -1305,6 +1315,8 @@ See also: :ref:`supervised_failover_overview_fault_tolerance`
 
 ..  confval:: failover.stateboard.keepalive_interval
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A time interval (in seconds) that specifies how long a transient state information is stored and how quickly a lock expires.
 
     ..  NOTE::
@@ -1320,6 +1332,8 @@ See also: :ref:`supervised_failover_overview_fault_tolerance`
 
 ..  confval:: failover.stateboard.renew_interval
 
+    **Since:** :doc:`3.1.0 </release/3.1.0>`.
+
     A time interval (in seconds) that specifies how often a failover coordinator writes its state information to etcd.
     This option also determines the frequency at which an active coordinator reads new commands from etcd.