title: EF Core ValueGeneratedOnAdd does not work with postgresql
body: <p>When using ConfigurationDbContext from <code>Assembly IdentityServer4.EntityFramework.Storage</code></p>
  
  <p>And seeding database with <code>IdentityServer4.Models.Client</code> entity
  <a href="https://i.stack.imgur.com/yKScj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yKScj.png" alt="enter image description here"></a></p>
  
  <p>I get the following error: <strong>PostgresException: 23502: null value in column "Id" violates not-null constraint</strong></p>
  
  <p>I took a look at the database and it turns out that the column is of type <code>integer</code>, even though I'd expect it to be <code>serial</code>.
  <a href="https://i.stack.imgur.com/rfqDZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rfqDZ.png" alt="enter image description here"></a></p>
  
  <p>Below you can see parts of migration code responsible for column creation:</p>
  
  <pre><code> migrationBuilder.CreateTable(
                  name: "Clients",
                  columns: table =&gt; new
                  {
                      Id = table.Column&lt;int&gt;(nullable: false)
                          .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
  </code></pre>
  
  <p>and</p>
  
  <pre><code>modelBuilder.Entity("IdentityServer4.EntityFramework.Entities.Client", b =&gt;
                  {
                      b.Property&lt;int&gt;("Id")
                          .ValueGeneratedOnAdd()
                          .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
  </code></pre>
  
  <p>Basing on documentation <a href="https://www.npgsql.org/efcore/value-generation.html" rel="nofollow noreferrer">https://www.npgsql.org/efcore/value-generation.html</a>,
  calling <code>ValueGeneratedOnAdd()</code> on a <code>integer</code> column should result in <code>serial</code> type in the database. </p>
  
  <p>Any thoughs on this?</p>