docs: rename external-auth heading in setup doc (#17868)

to help point searchers to the correct doc


[preview](https://coder.com/docs/@setup-ext-auth/admin/setup#continue-your-setup-with-external-authentication)

---------

Co-authored-by: EdwardAngert <17991901+EdwardAngert@users.noreply.github.com>

docs/admin/setup/index.md

@@ -140,7 +140,7 @@ To configure Coder behind a corporate proxy, set the environment variables
 `HTTP_PROXY` and `HTTPS_PROXY`. Be sure to restart the server. Lowercase values
 (e.g. `http_proxy`) are also respected in this case.
 
-## External Authentication
+## Continue your setup with external authentication
 
 Coder supports external authentication via OAuth2.0. This allows enabling
 integrations with Git providers, such as GitHub, GitLab, and Bitbucket.

docs/manifest.json

@@ -551,7 +551,7 @@
 					]
 				},
 				{
-					"title": "External Auth",
+					"title": "External Authentication",
 					"description": "Learn how to configure external authentication",
 					"path": "./admin/external-auth.md",
 					"icon_path": "./images/icons/plug.svg"