Message Table: Configure Column Header Name

## What?
Configuring column headers would be quite helpful for a better overview and to better reflect the domain of the log messages.

## Why?
For example, in a cloud environment, Graylog receives the field `filebeat_kubernetes_namespace.` For everyone
who knows the configuration of the Kubernetes environment, it might be clear that a client's name is used here (or something else). But if the user can reflect that in the message table, that would be beneficial.

## Your Environment
* Graylog Version: Graylog Cloud 6.1.8 (589)