error: Add SC_EEXIST for dups

Issue: 5748

This commit adds SC_EEXIST to be used for cases where an
item/resource/artifact with the same attributes already exists.

src/util-error.c

@@ -46,6 +46,7 @@ const char * SCErrorToString(SCError err)
         CASE_CODE(SC_ENOMEM);
         CASE_CODE(SC_EINVAL);
         CASE_CODE(SC_ELIMIT);
+        CASE_CODE(SC_EEXIST);
 
         CASE_CODE (SC_ERR_MAX);
     }

src/util-error.h

@@ -29,6 +29,7 @@ typedef enum {
     SC_ENOMEM,
     SC_EINVAL,
     SC_ELIMIT,
+    SC_EEXIST,
 
     SC_ERR_MAX
 } SCError;