Added notes for packaging changes around security

ReleaseNotes

 For new logging deployement : 
 $SystemLogSocketIgnoreMsgTimestamp off
 
+  Package changes
+  ---------------
+  - castor-csec has been dropped: the GSI plugin has been removed whereas the KRB5 plugin
+    has been integrated into castor-lib, so that it is also part of the client distribution.
+    Therefore, as of this release the castor-lib RPM has a depency on Kerberos libraries.
 
 
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