ValuePath in value action handler shows String object as part of the path

## Expected Behavior
Value path should show correct value
## Current Behavior
When the user has the same field as column Pivot and Row pivot one of the value path parts shows String instead of the real value.

## Steps to Reproduce (for bugs)
1. Create an aggregation widget with the same field in row and column pivots f.e. `resource`

2. F.e. you can add some console logs on clicking the copy to clipboard action to show all parameters which receive handler
3. click on the action

4. check the console

5. Value path shows String as one of the value

## Context
I need the correct behavior of this property to finish [issue](https://github.com/Graylog2/graylog2-server/issues/14544)

## Your Environment

* Graylog Version:
* Java Version:
* Elasticsearch Version:
* MongoDB Version:
* Operating System:
* Browser version: