chore: move /gitauth to /externalauth on the frontend (#9954)

* chore: move `/gitauth` to `/externalauth` on the frontend

This actually took a lot more jank than anticipated,
so I wanted to split this up before adding the ability
to embed new providers.

* Rename FE

* Fix em' up

* Fix linting error

* Fix e2e tests

* chore: update helm golden files

coderd/httpmw/externalauthparam_test.go

@@ -0,0 +1,49 @@
+package httpmw_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/coderd/externalauth"
+	"github.com/coder/coder/v2/coderd/httpmw"
+)
+
+//nolint:bodyclose
+func TestExternalAuthParam(t *testing.T) {
+	t.Parallel()
+	t.Run("Found", func(t *testing.T) {
+		t.Parallel()
+		routeCtx := chi.NewRouteContext()
+		routeCtx.URLParams.Add("externalauth", "my-id")
+		r := httptest.NewRequest(http.MethodGet, "/", nil)
+		r = r.WithContext(context.WithValue(r.Context(), chi.RouteCtxKey, routeCtx))
+		res := httptest.NewRecorder()
+
+		httpmw.ExtractExternalAuthParam([]*externalauth.Config{{
+			ID: "my-id",
+		}})(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			require.Equal(t, "my-id", httpmw.ExternalAuthParam(r).ID)
+			w.WriteHeader(http.StatusOK)
+		})).ServeHTTP(res, r)
+
+		require.Equal(t, http.StatusOK, res.Result().StatusCode)
+	})
+
+	t.Run("NotFound", func(t *testing.T) {
+		t.Parallel()
+		routeCtx := chi.NewRouteContext()
+		routeCtx.URLParams.Add("externalauth", "my-id")
+		r := httptest.NewRequest(http.MethodGet, "/", nil)
+		r = r.WithContext(context.WithValue(r.Context(), chi.RouteCtxKey, routeCtx))
+		res := httptest.NewRecorder()
+
+		httpmw.ExtractExternalAuthParam([]*externalauth.Config{})(nil).ServeHTTP(res, r)
+
+		require.Equal(t, http.StatusNotFound, res.Result().StatusCode)
+	})
+}