added xml comments for existing api parts and pieces.

server/Filters/ApiVersionOperationFilter.cs

@@ -0,0 +1,20 @@
+using Microsoft.OpenApi.Any;
+using Microsoft.OpenApi.Models;
+using Swashbuckle.AspNetCore.SwaggerGen;
+
+namespace server.Filters
+{
+    public class ApiVersionOperationFilter : IOperationFilter
+    {
+        public void Apply(OpenApiOperation operation, OperationFilterContext context)
+        {
+            var headerParameter = operation.Parameters.Where(p => p.Name == "x-api-version").SingleOrDefault();
+            
+            if (headerParameter != null)
+            {
+                headerParameter.Description = "Header value that identifies target version of api.";
+                headerParameter.Schema.Default = new OpenApiString(context.DocumentName.ToLower().Replace("v", ""));
+            }
+        }
+    }
+}