aj/support log tags

[astuyve]

Fixes #515

You can reproduce by creating a new lambda function, enabling JSON logs in Lambda, and then logging something like this:

  console.log({ddtags: 'aj:test,aj_type:added_tags', message: {input: event, more_items: "are working"}});

You should be able to search for those tags in the app:

[duncanista]

This looks great, I'd like to see the performance implications of trying to parse every message into a json object, I'd expect serde to do a great job here already tho