Improve Administraion > Configuration documentation page

[hichamelkaddioui]

Currently, the documentation for server configuration provides directions for editing config options for MediaBrowser.Controller.Extensions but contains no pointers on how to edit some Jellyfin's internals like MediaBrowser.Model.Configuration options.

From my understanding these values can be set by editing XML files in the config folder, e.g. config/system.xml provides values for MediaBrowser.Model.Configuration which take precedence over code's defaults. It also seems this is the only way an admin could set some of these values, as

• ServerConfiguration.cs doesn't seem to be using Microsoft.Extensions.Configuration and hence cannot provide JELLYFIN_* environment variables;
• the web client doesn't have an entry for every option, e.g. ImageExtractionTimeoutMs.

The documentation could provide more information about these XML files.

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In addition, the Main Configuration Options section doesn't list all the configuration keys in MediaBrowser.Controller.Extensions.ConfigurationExtensions

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I'll try to draft a PR soon :)