Add new param to filter_parser doc

Signed-off-by: Athish Pranav D <athishanna@gmail.com>

pipeline/filters/parser.md

@@ -12,6 +12,7 @@ The plugin supports the following configuration parameters:
 | Parser | Specify the parser name to interpret the field. Multiple _Parser_ entries are allowed \(one per line\). |  |
 | Preserve\_Key | Keep original `Key_Name` field in the parsed result. If false, the field will be removed. | False |
 | Reserve\_Data | Keep all other original fields in the parsed result. If false, all other original fields will be removed. | False |
+| Hash_Value_Field | Stores the parsed values as a hash value in a field. | False |
 
 ## Getting Started