Add support to tag events when parse_json fails to parse

[kkondaka]

Is your feature request related to a problem? Please describe.
Add support to tag events when parse_json fails to parse. This is sub-issue of issue #629.

Describe the solution you'd like
Solution is to add option to parse_json processor that can add tags on failure. The proposed config is

processor:                                                                                                                                              
     - parse_json:                                                                                                                                        
          source: "log"                                                                                                                                     
          tags_on_failure: ["json_parse_fail", "tag2"]    

This config would add the specified tags to the event upon parse failure.

Describe alternatives you've considered (Optional)
A clear and concise description of any alternative solutions or features you've considered.

Additional context
The added tags may be used to in the pipeline to do conditional routing or conditional processing.