Show all fields on message "permalink" page

## What?

It should be possible to show all fields (including Graylog internal, e.g. `gl2_remote_ip`) on the message "permalink" page (`/messages/$INDEX/$MESSAGE_GUID`).

## Why?

A user can customize widgets to display useful fields that are hidden by default (e.g. `gl2_remote_ip`, `gl2_accounted_message_size`), however it's not possible to see these fields in the message permalink page UI.

Since the full message, with all of its fields, already gets returned from the API call (`/api/messages/$INDEX/$MESSAGE_GUID`), it would be nice if the message permalink page simply displayed all fields, or provided a toggle that allowed the user to display all fields.

## Your Environment

* Graylog Version: `6.1.8`