Add Metrics and Plugins properties to test class

Added two properties, `Metrics` and `Plugins`, to the
`FlowSynxServiceCollectionExtensionsTests` class. Both
properties throw a `NotImplementedException` when accessed.

#57

Author: ziagham

tests/FlowSynx.Client.AspNetCore.UnitTests/FlowSynxServiceCollectionExtensionsTests.cs

@@ -121,6 +121,8 @@ public void SetAuthenticationStrategy(IAuthenticationStrategy strategy)
 
         public ILogsService Logs => throw new NotImplementedException();
 
+        public IMetricsService Metrics => throw new NotImplementedException();
+
         public IPluginsService Plugins => throw new NotImplementedException();
 
         public IWorkflowsService Workflows => throw new NotImplementedException();