Hyperlink a decorated field, or pipeline field

## Hello, I would like hyperlink an url constructed by a pipeline, or a decorator: format string

## Why?

When message incoming raw, and need decorator, It can be interesting to access all decorator featured after extrator work.
Here is my case:

I have message splited, and constructed in graylog.
- First, I split all fields needed with an extractor GROK. --> ok
- Second, I create a pipeline to create a field url and concatenate other fields extracted. / or by a decorator --> ok
- Third, I would like hyperlink this url --> KO

If I use 2 decorator: order is correct:

## Your Environment

* Graylog Version: 3.3
* Elasticsearch Version: 5
* MongoDB Version:
* Operating System: OL7
* Browser version: Chrome