Advertise WebAuthn support (#29176)

This well-known indicates for password manager, that passkeys are supported.

source:
https://android-developers.googleblog.com/2023/10/make-passkey-endpoints-well-known-url-part-of-your-passkey-implementation.html

spec:
https://github.com/ms-id-standards/MSIdentityStandardsExplainers/blob/main/PasskeyEndpointsWellKnownUrl/explainer.md

routers/web/web.go

@@ -473,6 +473,7 @@ func registerRoutes(m *web.Route) {
 		m.Get("/change-password", func(ctx *context.Context) {
 			ctx.Redirect(setting.AppSubURL + "/user/settings/account")
 		})
+		m.Get("/passkey-endpoints", passkeyEndpoints)
 		m.Methods("GET, HEAD", "/*", public.FileHandlerFunc())
 	}, optionsCorsHandler())