Add allowed_auxiliary_paths to default server.conf file

[danotorrey]

Description

Add a sample configuration for the allowed_auxiliary_paths configuration property in the default graylog.conf file, which was originally added in #10244

Documentation has also been provided in Graylog2/documentation#1185.

Motivation and Context

This configuration property was discussed yesterday in the context of investigating a Cloud-related issue. I thought that it would be good to provide a sample configuration and documentation for this property, so that others can see a description for the property and an example for how to configure it.

How Has This Been Tested?

No testing needed. Just static file changes in the default graylog.conf, which are commented out.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [*] My code follows the code style of this project.
• [*] My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.