[BUG] Cannot use Elsa: `Scheme already exists: Bearer`

## Description
When trying to startup after following the Server docs. I receive the following exception:

```
System.InvalidOperationException: Scheme already exists: Bearer
at Microsoft.AspNetCore.Authentication.AuthenticationOptions.AddScheme(String name, Action`1 configureBuilder)
at Microsoft.Extensions.Options.ConfigureNamedOptions`1.Configure(String name, TOptions options)
at Microsoft.Extensions.Options.OptionsFactory`1.Create(String name)
at Microsoft.Extensions.Options.UnnamedOptionsManager`1.get_Value()
at Microsoft.AspNetCore.Authentication.AuthenticationSchemeProvider..ctor(IOptions`1 options, IDictionary`2 schemes)
at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
at System.Reflection.MethodBaseInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs, BindingFlags invokeAttr)
at System.Reflection.MethodBaseInvoker.InvokeWithOneArg(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(ServiceIdentifier serviceIdentifier)
at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(ServiceIdentifier serviceIdentifier, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
at Microsoft.Extensions.Internal.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider)
at Microsoft.Extensions.Internal.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)
at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.ReflectionMiddlewareBinder.CreateMiddleware(RequestDelegate next)
at Microsoft.AspNetCore.Builder.ApplicationBuilder.Build()
at Microsoft.AspNetCore.Hosting.GenericWebHostService.StartAsync(CancellationToken cancellationToken)
at Microsoft.Extensions.Hosting.Internal.Host.b__15_1(IHostedService service, CancellationToken token)
at Microsoft.Extensions.Hosting.Internal.Host.ForeachService[T](IEnumerable`1 services, CancellationToken token, Boolean concurrent, Boolean abortOnFirstException, List`1 exceptions, Func`3 operation)
at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
at Buzzscreens.Program.Main(String[] args) in
```

I'm honestly not sure what else needs to be fiddled with here to make this work :/

```cs
public static IServiceCollection Install(IServiceCollection services, AppConfig appConfig)
{
services.AddElsa(elsa =>
{
// Configure Management layer to use EF Core.
elsa.UseWorkflowManagement(management =>
management.UseEntityFrameworkCore(ef => ef.UsePostgreSql(appConfig.DbConnectionString)));

// Configure Runtime layer to use EF Core.
elsa.UseWorkflowRuntime(runtime => runtime.UseEntityFrameworkCore(ef => ef.UsePostgreSql(appConfig.DbConnectionString)));

// Default Identity features for authentication/authorization.
elsa.UseIdentity(identity =>
{
identity.TokenOptions = options =>
options.SigningKey = "sufficiently-large-secret-signing-key"; // This key needs to be at least 256 bits long.
identity.UseAdminUserProvider();
});

// Configure ASP.NET authentication/authorization.
elsa.UseDefaultAuthentication(auth => auth.UseAdminApiKey());

// Expose Elsa API endpoints.
elsa.UseWorkflowsApi();

// Setup a SignalR hub for real-time updates from the server.
elsa.UseRealTimeWorkflows();

// Enable C# workflow expressions
elsa.UseCSharp();

// Enable HTTP activities.
elsa.UseHttp();

// Use timer activities.
elsa.UseScheduling();

// Register custom activities from the application, if any.
elsa.AddActivitiesFrom();

// Register custom workflows from the application, if any.
elsa.AddWorkflowsFrom();
});
return services;
}
```