Create a struct with all of Hugo's config options

Primary motivation is documentation, but it will also hopefully simplify the code.

Also,

* Lower case the default output format names; this is in line with the custom ones (map keys) and how
it's treated all the places. This avoids doing `stringds.EqualFold` everywhere.

Closes #10896
Closes #10620

resources/resource_factories/create/remote.go

@@ -197,7 +197,7 @@ func (c *Client) FromRemote(uri string, optionsm map[string]any) (resource.Resou
 		}
 
 		// Now resolve the media type primarily using the content.
-		mediaType = media.FromContent(c.rs.MediaTypes, extensionHints, body)
+		mediaType = media.FromContent(c.rs.MediaTypes(), extensionHints, body)
 
 	}