feat: add github device flow for authentication (#8232)

* feat: add github device flow for authentication

This will allow us to add a GitHub OAuth provider out-of-the-box
to reduce setup requirements.

* Improve askpass view

* Add routes to improve clarity of git auth

* Redesign the git auth page

* Refactor to add a page view

* Fix sideways layout

* Remove legacy notify

* Fix git auth redirects

* Add E2E tests

* Fix route documentation

* Fix imports

* Remove unused imports

* Fix E2E web test

* Fix friendly message appearance

* Fix layout shifting for full-screen sign-in

* Fix height going to 100%

* Fix comments

cli/cliui/gitauth_test.go

@@ -2,7 +2,6 @@ package cliui_test
 
 import (
 	"context"
-	"net/url"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -33,7 +32,7 @@ func TestGitAuth(t *testing.T) {
 						ID:              "github",
 						Type:            codersdk.GitProviderGitHub,
 						Authenticated:   fetched.Load(),
-						AuthenticateURL: "https://example.com/gitauth/github?redirect=" + url.QueryEscape("/gitauth?notify"),
+						AuthenticateURL: "https://example.com/gitauth/github",
 					}}, nil
 				},
 				FetchInterval: time.Millisecond,