Dont register redis watcher if the redis service is not bound into the container.

[mad-briller]

When installing Telescope into a Laravel application which has opted out of Redis support by removing the RedisServiceProvider in app.php, a BindingResolutionException is thrown during auto-discovery:

 ⇒  composer require --dev laravel/telescope
Info from https://repo.packagist.org: #StandWithUkraine
Using version ^4.9 for laravel/telescope
./composer.json has been updated
Running composer update laravel/telescope
Loading composer repositories with package information
Updating dependencies
Lock file operations: 1 install, 0 updates, 0 removals
  - Locking laravel/telescope (v4.9.4)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 1 install, 0 updates, 0 removals
  - Downloading laravel/telescope (v4.9.4)
  - Installing laravel/telescope (v4.9.4): Extracting archive
Generating optimized autoload files
> Illuminate\Foundation\ComposerScripts::postAutoloadDump
> @php artisan package:discover --ansi

   Illuminate\Contracts\Container\BindingResolutionException

  Target class [redis] does not exist.

  at vendor/laravel/framework/src/Illuminate/Container/Container.php:877
    873▕
    874▕         try {
    875▕             $reflector = new ReflectionClass($concrete);
    876▕         } catch (ReflectionException $e) {
  ➜ 877▕             throw new BindingResolutionException("Target class [$concrete] does not exist.", 0, $e);
    878▕         }
    879▕
    880▕         // If the type is not instantiable, the developer is attempting to resolve
    881▕         // an abstract type such as an Interface or Abstract Class and there is

  1   [internal]:0
      Illuminate\Foundation\Application::Illuminate\Foundation\{closure}(Object(Laravel\Telescope\TelescopeServiceProvider))

      +18 vendor frames
  20  [internal]:0
      Illuminate\Foundation\Application::Illuminate\Foundation\{closure}(Object(Laravel\Telescope\TelescopeServiceProvider))
Script @php artisan package:discover --ansi handling the post-autoload-dump event returned with error code 1

This can be prevented by disabling the watcher using a .env value, or modifying the telescope.php config file, but a user who is installing Telescope for the first time wont expect to have to do such a thing to get it working.

This pr makes the RedisWatcher register itself only when redis is bound into the application container to avoid this issue.

Thanks for your time.