Add blog to docs (#484)

* Adding social card infrastructure
* Upgrades doc project to .NET 6
* Adds Playwright
* Changes the console to a web project for Playwright
* Adds social card template
* Added blog content
* Parallelized social image processing
* Updating CI to use .NET 6 for docs build

docs/input/blog/category.cshtml

@@ -0,0 +1,14 @@
+@inherits StatiqRazorPage<IDocument>
+@if (Document.ContainsKey(Keys.GroupKey))
+{
+  @Html.Partial("_posts.cshtml", Document.GetChildren())
+  @Html.Partial("_nextprevious.cshtml", Document)
+}
+else
+{
+    @foreach (var tag in Document.GetChildren().OrderByDescending(x => x.GetChildren().Count()))
+    {
+        var postCount = tag.GetChildren().Count().ToString();
+        <a role="button" href="@Context.GetLink(tag)" class="badge badge-light"> @tag.GetTitle() (@postCount)</a>
+    }
+}