Code changes for IOptionsMonitor demo

HomeController.cs

// MailFeatureOptions.cs
public class MailFeatureOptions
{
    public bool IsEnabled { get; set; }
    public string SmtpServer { get; set; }
    public string FromEmailAddress { get; set; }
    public string Subject { get; set; }
}

// Startup.cs
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        // some other code...
        services.Configure<MailFeatureOptions>(Configuration.GetSection(nameof(MailFeatureOptions)));
        services.AddControllersWithViews();
    }

    // some other code...
}


// HomeController.cs
public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;
    private readonly IOptionsMonitor<MailFeatureOptions> mailFeatureOptionsMonitor;

    public HomeController(ILogger<HomeController> logger, IOptionsMonitor<MailFeatureOptions> mailFeatureOptionsMonitor)
    {
        _logger = logger;
        this.mailFeatureOptionsMonitor = mailFeatureOptionsMonitor;
    }

    public IActionResult Index()
    {
        // Load in ViewData
        ViewData["IsEnabled"] = this.mailFeatureOptionsMonitor.CurrentValue.IsEnabled;
        ViewData["SmtpServer"] = this.mailFeatureOptionsMonitor.CurrentValue.SmtpServer;
        ViewData["FromEmailAddress"] = this.mailFeatureOptionsMonitor.CurrentValue.FromEmailAddress;
        ViewData["Subject"] = this.mailFeatureOptionsMonitor.CurrentValue.Subject;
        return View();
    }
}

// Views/Home/Index.cshtml
<div class="card" style="width: 58rem;">
    <div class="card-header">
        MailFeatureOptions
    </div>

    <div class="card-body">
        <ul class="list-group list-group-flush">
            <li class="list-group-item text-left"><strong>IsEnabled:</strong> @ViewData["IsEnabled"]</li>
            <li class="list-group-item text-left"><strong>SmtpServer:</strong> @ViewData["SmtpServer"]</li>
            <li class="list-group-item text-left"><strong>FromEmailAddress:</strong> @ViewData["FromEmailAddress"]</li>
            <li class="list-group-item text-left"><strong>Subject: </strong>@ViewData["Subject"]</li>
        </ul>
    </div>
</div>