docs: move custom subpath guide to configuration section

docs/docs.json

@@ -221,7 +221,6 @@
             "pages": [
               "self-hosting/setup/one-click",
               "self-hosting/setup/docker",
-              "self-hosting/setup/custom-subpath",
               "self-hosting/setup/monitoring",
               "self-hosting/setup/cluster-setup",
               "self-hosting/setup/kubernetes"
@@ -231,6 +230,7 @@
             "group": "Configuration",
             "pages": [
               "self-hosting/configuration/custom-ssl",
+              "self-hosting/configuration/custom-subpath",
               "self-hosting/configuration/environment-variables",
               "self-hosting/configuration/smtp",
               "self-hosting/configuration/file-uploads",