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/convert_test.go

@@ -17,6 +17,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/spf13/cast"
+
 	"github.com/gohugoio/hugo/markup/goldmark/goldmark_config"
 
 	"github.com/gohugoio/hugo/markup/highlight"
@@ -193,6 +195,103 @@ func TestConvertAutoIDBlackfriday(t *testing.T) {
 	c.Assert(got, qt.Contains, "<h2 id=\"let-s-try-this-shall-we\">")
 }
 
+func TestConvertAttributes(t *testing.T) {
+	c := qt.New(t)
+
+	withBlockAttributes := func(conf *markup_config.Config) {
+		conf.Goldmark.Parser.Attribute.Block = true
+		conf.Goldmark.Parser.Attribute.Title = false
+	}
+
+	withTitleAndBlockAttributes := func(conf *markup_config.Config) {
+		conf.Goldmark.Parser.Attribute.Block = true
+		conf.Goldmark.Parser.Attribute.Title = true
+	}
+
+	for _, test := range []struct {
+		name       string
+		withConfig func(conf *markup_config.Config)
+		input      string
+		expect     interface{}
+	}{
+		{
+			"Title",
+			nil,
+			"## heading {#id .className attrName=attrValue class=\"class1 class2\"}",
+			"<h2 id=\"id\" class=\"className class1 class2\" attrName=\"attrValue\">heading</h2>\n",
+		},
+		{
+			"Blockquote",
+			withBlockAttributes,
+			"> foo\n> bar\n{#id .className attrName=attrValue class=\"class1 class2\"}\n",
+			"<blockquote id=\"id\" class=\"className class1 class2\"><p>foo\nbar</p>\n</blockquote>\n",
+		},
+		{
+			"Paragraph",
+			withBlockAttributes,
+			"\nHi there.\n{.myclass }",
+			"<p class=\"myclass\">Hi there.</p>\n",
+		},
+		{
+			"Ordered list",
+			withBlockAttributes,
+			"\n1. First\n2. Second\n{.myclass }",
+			"<ol class=\"myclass\">\n<li>First</li>\n<li>Second</li>\n</ol>\n",
+		},
+		{
+			"Unordered list",
+			withBlockAttributes,
+			"\n* First\n* Second\n{.myclass }",
+			"<ul class=\"myclass\">\n<li>First</li>\n<li>Second</li>\n</ul>\n",
+		},
+		{
+			"Unordered list, indented",
+			withBlockAttributes,
+			`* Fruit
+  * Apple
+  * Orange
+  * Banana
+  {.fruits}
+* Dairy
+  * Milk
+  * Cheese
+  {.dairies}
+{.list}`,
+			[]string{"<ul class=\"list\">\n<li>Fruit\n<ul class=\"fruits\">", "<li>Dairy\n<ul class=\"dairies\">"},
+		},
+		{
+			"Table",
+			withBlockAttributes,
+			`| A        | B           |
+| ------------- |:-------------:| -----:|
+| AV      | BV |
+{.myclass }`,
+			"<table class=\"myclass\">\n<thead>",
+		},
+		{
+			"Title and Blockquote",
+			withTitleAndBlockAttributes,
+			"## heading {#id .className attrName=attrValue class=\"class1 class2\"}\n> foo\n> bar\n{.myclass}",
+			"<h2 id=\"id\" class=\"className class1 class2\" attrName=\"attrValue\">heading</h2>\n<blockquote class=\"myclass\"><p>foo\nbar</p>\n</blockquote>\n",
+		},
+	} {
+		c.Run(test.name, func(c *qt.C) {
+			mconf := markup_config.Default
+			if test.withConfig != nil {
+				test.withConfig(&mconf)
+			}
+			b := convert(c, mconf, test.input)
+			got := string(b.Bytes())
+
+			for _, s := range cast.ToStringSlice(test.expect) {
+				c.Assert(got, qt.Contains, s)
+			}
+
+		})
+	}
+
+}
+
 func TestConvertIssues(t *testing.T) {
 	c := qt.New(t)