table: Add TABLE_SET_JSON_FIELD_NAME

Lets you conveniently set JSON field names in table_add_many. Especially
useful for vertical tables. For example:

table_add_many(t,
               TABLE_FIELD, "Display Name",
               TABLE_STRING, obj->display_name,
               TABLE_SET_JSON_FIELD_NAME, "displayName",
               TABLE_FIELD, "Timestamp",
               TABLE_TIMESTAMP, obj->timestamp,
               TABLE_SET_JSON_FIELD_NAME, "timestampUSec");

src/shared/format-table.c

@@ -1184,6 +1184,20 @@ int table_add_many_internal(Table *t, TableDataType first_type, ...) {
                         goto check;
                 }
 
+                case TABLE_SET_JSON_FIELD_NAME: {
+                        const char *n = va_arg(ap, const char*);
+                        size_t idx;
+                        if (t->vertical) {
+                                assert(TABLE_CELL_TO_INDEX(last_cell) >= t->n_columns);
+                                idx = TABLE_CELL_TO_INDEX(last_cell) / t->n_columns - 1;
+                        } else {
+                                idx = TABLE_CELL_TO_INDEX(last_cell);
+                                assert(idx < t->n_columns);
+                        }
+                        r = table_set_json_field_name(t, idx, n);
+                        goto check;
+                }
+
                 case _TABLE_DATA_TYPE_MAX:
                         /* Used as end marker */
                         va_end(ap);