commands: Create new 'hugo list all' command

New:
- command `hugo list all`, return all posts meta in csv format

Refactoring:
- move common parts in commands/list.go to function `buildSites`
- change way to detect path to content

See #5904

commands/list_test.go

@@ -0,0 +1,70 @@
+package commands
+
+import (
+	"bytes"
+	"encoding/csv"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/require"
+)
+
+func captureStdout(f func() (*cobra.Command, error)) (string, error) {
+	old := os.Stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w
+
+	_, err := f()
+
+	if err != nil {
+		return "", err
+	}
+
+	w.Close()
+	os.Stdout = old
+
+	var buf bytes.Buffer
+	io.Copy(&buf, r)
+	return buf.String(), nil
+}
+
+func TestListAll(t *testing.T) {
+	assert := require.New(t)
+	dir, err := createSimpleTestSite(t, testSiteConfig{})
+
+	assert.NoError(err)
+
+	hugoCmd := newCommandsBuilder().addAll().build()
+	cmd := hugoCmd.getCommand()
+
+	defer func() {
+		os.RemoveAll(dir)
+	}()
+
+	cmd.SetArgs([]string{"-s=" + dir, "list", "all"})
+
+	out, err := captureStdout(cmd.ExecuteC)
+	assert.NoError(err)
+
+	r := csv.NewReader(strings.NewReader(out))
+
+	header, err := r.Read()
+	assert.NoError(err)
+
+	assert.Equal([]string{
+		"path", "slug", "title",
+		"date", "expiryDate", "publishDate",
+		"draft", "permalink",
+	}, header)
+
+	record, err := r.Read()
+	assert.Equal([]string{
+		filepath.Join("content", "p1.md"), "", "P1",
+		"0001-01-01T00:00:00Z", "0001-01-01T00:00:00Z", "0001-01-01T00:00:00Z",
+		"false", "https://example.org/p1/",
+	}, record)
+}