Change ConnectionDetails.gcGracePeriod to ConnectionDetails.objectsGCGracePeriod

The previous `gcGracePeriod` name was never used in production so we can
update the spec without deleting the old spec points

Author: VeskeR

textile/features.textile

@@ -1828,7 +1828,7 @@ h4. ConnectionDetails
 ** @(CD2f)@ @connectionStateTtl@ is the duration that Ably will persist the connection state when a Realtime client is abruptly disconnected
 ** @(CD2g)@ @serverId@ string is a unique identifier for the front-end server that the client has connected to. This server ID is only used for the purposes of debugging
 ** @(CD2h)@ @maxIdleInterval@ is the maximum length of time in milliseconds that the server will allow no activity to occur in the server->client direction. After such a period of inactivity, the server will send a @HEARTBEAT@ or transport-level ping to the client. If the value is 0, the server will allow arbitrarily-long levels of inactivity.
-** @(CD2i)@ @gcGracePeriod@ number is the length of time, in milliseconds, that the client library must wait before releasing resources for tombstoned objects and map entries (see "RTO10":../objects-features#RTO10)
+** @(CD2i)@ @objectsGCGracePeriod@ integer - the length of time, in milliseconds, that the client library must wait before releasing resources for tombstoned objects and map entries (see "RTO10":../objects-features#RTO10)
 h4. ChannelProperties
 * @(CP1)@ properties of a channel and its state
 * @(CP2)@ The attributes of @ChannelProperties@ consist of:
@@ -2541,7 +2541,7 @@ class ConnectionDetails: // CD*, internal
   maxMessageSize: Int // CD2c
   serverId: String // CD2g
   maxIdleInterval: Duration // CD2h
-  gcGracePeriod: Int // CD2i
+  objectsGCGracePeriod: Int // CD2i
 
 class Message: // TM*
   constructor(name: String?, data: Data?) // TM4

textile/objects-features.textile

@@ -90,9 +90,9 @@ h3(#realtime-objects). RealtimeObjects
 * @(RTO10)@ The client library must have a process in place to regularly check for objects and map entries that have been tombstoned for a period of time, and release their resources so they can be garbage collected. Tombstoned objects and map entries are retained in memory for a sufficient grace period (at least >2 minutes) to ensure that no late-arriving operation is mistakenly applied to an object or map entry the client has already "forgotten" about.
 ** @(RTO10a)@ The check should occur at regular intervals, for example, every 5 minutes
 ** @(RTO10b)@ The grace period for releasing resources for tombstoned objects and map entries is determined as follows:
-*** @(RTO10b1)@ It is equal to "@ConnectionDetails.gcGracePeriod@":../features#CD2i received in the @CONNECTED@ @ProtocolMessage@
-*** @(RTO10b2)@ The grace period value is updated to match the new @ConnectionDetails.gcGracePeriod@ value whenever a new @CONNECTED@ @ProtocolMessage@ is received per "RTN24":../features#RTN24
-*** @(RTO10b3)@ A default value of 86,400,000 milliseconds (24 hours) is used if @ConnectionDetails.gcGracePeriod@ is not provided
+*** @(RTO10b1)@ It is equal to "@ConnectionDetails.objectsGCGracePeriod@":../features#CD2i received in the @CONNECTED@ @ProtocolMessage@
+*** @(RTO10b2)@ The grace period value is updated to match the new @ConnectionDetails.objectsGCGracePeriod@ value whenever a new @CONNECTED@ @ProtocolMessage@ is received per "RTN24":../features#RTN24
+*** @(RTO10b3)@ A default value of 86,400,000 milliseconds (24 hours) is used if @ConnectionDetails.objectsGCGracePeriod@ is not provided
 ** @(RTO10c)@ On each check interval:
 *** @(RTO10c1)@ For each @LiveObject@ in the @ObjectsPool@:
 **** @(RTO10c1a)@ Check if the @LiveObject@ needs to release any resources, see "RTLM19":#RTLM19