fix: always generate docs for the sample project

This is required because the swagger integration is configured to always extract descriptions/schemas from the generated documentation file. When this file does't exist, we get a FileNotFoundException at the startup phase.

Author: guilhermeluizsp

samples/Liquid.Sample.CarRegistry/Liquid.Sample.CarRegistry.csproj

@@ -10,8 +10,8 @@
     <AssemblyName>Liquid.Sample.CarRegistry</AssemblyName>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
-    <DocumentationFile>bin\Debug\netcoreapp2.2\Sample.Car.xml</DocumentationFile>
+  <PropertyGroup>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
   </PropertyGroup>
 
   <ItemGroup>