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/_posts.cshtml

@@ -0,0 +1,33 @@
+@inherits StatiqRazorPage<IEnumerable<IDocument>>
+@foreach (var post in Model)
+{
+    <div>
+        <h3 class="mb-0"><a href="@Context.GetLink(post)">@post.GetString("Title")</a></h3>
+        @{
+            var author = post.GetString("Author");
+            var published = post.GetDateTime("Published");
+            var category = post.GetString("Category");
+        }
+        <div class="mt-2 font-light text-xs md:text-sm">
+            <span>Posted </span>
+            @if (published != default(DateTime)) {
+                <span>@published.ToLongDateString() </span>
+            }
+            @if (author != null) {
+                <span>by @author </span>
+            }
+            @if (category != null) {
+                var categoryUrl = @Context.GetLink($"blog/{NormalizedPath.OptimizeFileName(category)}/index.html");
+                <span>
+                    to <a class="text-blue-800 underline" href="@categoryUrl">
+                        @category
+                    </a>
+                </span>
+            }
+
+        </div>
+        <article>
+            @Html.Raw(@post.GetString("Excerpt"))
+        </article>
+    </div>
+}