markup/goldmark: Add attributes support for blocks (tables etc.)

E.g.:

```
> foo
> bar
{.myclass}
```

There are some current limitations: For tables you can currently only apply it to the full table, and for lists the ul/ol-nodes only, e.g.:

```
* Fruit
  * Apple
  * Orange
  * Banana
  {.fruits}
* Dairy
  * Milk
  * Cheese
  {.dairies}
{.list}
```

Fixes #7548

markup/goldmark/goldmark_config/config.go

@@ -37,7 +37,10 @@ var Default = Config{
 	Parser: Parser{
 		AutoHeadingID:     true,
 		AutoHeadingIDType: AutoHeadingIDTypeGitHub,
-		Attribute:         true,
+		Attribute: ParserAttribute{
+			Title: true,
+			Block: false,
+		},
 	},
 }
 
@@ -82,5 +85,12 @@ type Parser struct {
 	AutoHeadingIDType string
 
 	// Enables custom attributes.
-	Attribute bool
+	Attribute ParserAttribute
+}
+
+type ParserAttribute struct {
+	// Enables custom attributes for titles.
+	Title bool
+	// Enables custom attributeds for blocks.
+	Block bool
 }