Update query operation enum and add EXECUTE

Changed the query operation enum to contain implicit enum values instead
of providing. The operation was never used as a bitmask so it is pointless
to declare them as such.

Added the EXECUTE type to the enum and used it in qc_sqlite and
qc_mysqlembedded.

query_classifier/qc_mysqlembedded/qc_mysqlembedded.cc

@@ -1745,6 +1745,10 @@ int32_t qc_mysql_get_operation(GWBUF* querybuf, int32_t* operation)
                     *operation = QUERY_OP_REVOKE;
                     break;
 
+                case SQLCOM_EXECUTE:
+                    *operation = QUERY_OP_EXECUTE;
+                    break;
+
                 default:
                     *operation = QUERY_OP_UNDEFINED;
                 }