Add Allowed Auxiliary Paths documentation for the CSV File Adapter

[danotorrey]

In Graylog 4.1, a new server.conf configuration property named allowed_auxiliary_paths was added. The documentation needs to be adjusted accordingly. PR https://github.com/Graylog2/graylog2-server/pull/10391 has more info about the property.

Context

The new property was primarily needed for Graylog Cloud, but since it is included in the server core, the documentation should be updated.

Expected Content

• The property should be listed with a description on the Configure > server.conf page. The property is a general one, that eventually will be used by other parts of the application, so the description should probably indicate that it's currently used by the CSV File Adapter, but might be used for other areas in the future.
• Update the CSV File Adapter page to indicate that it uses the new configuration property, and perhaps point to the server.conf page page.

Your Environment

• Graylog Version: 4.1