[MM-17155] Changes to email notifications to support Deep Linking page (#13362)

* Change link to redirect email notifications to landing page

* Fix to undefined variable

* Change `vault` to `landing`

* Added a couple tests

Co-authored-by: David Meza <dmeza@users.noreply.github.com>
Co-authored-by: mattermod <mattermod@users.noreply.github.com>

app/notification_email_test.go

@@ -586,3 +586,50 @@ func TestGenerateHyperlinkForChannelsPrivate(t *testing.T) {
 	outMessage := th.App.generateHyperlinkForChannels(message, teamName, teamURL)
 	assert.Equal(t, message, outMessage)
 }
+
+func TestLandingLink(t *testing.T) {
+	th := Setup(t)
+	defer th.TearDown()
+
+	recipient := &model.User{}
+	post := &model.Post{
+		Message: "This is the message",
+	}
+	channel := &model.Channel{
+		DisplayName: "ChannelName",
+		Type:        model.CHANNEL_OPEN,
+	}
+	channelName := "ChannelName"
+	senderName := "sender"
+	teamName := "select_team"
+	teamURL := "http://localhost:8065/landing#/" + teamName
+	emailNotificationContentsType := model.EMAIL_NOTIFICATION_CONTENTS_FULL
+	translateFunc := utils.GetUserTranslations("en")
+
+	body := th.App.getNotificationEmailBody(recipient, post, channel, channelName, senderName, teamName, teamURL, emailNotificationContentsType, true, translateFunc)
+	require.Contains(t, body, teamURL, fmt.Sprintf("Expected email text '%s'. Got %s", teamURL, body))
+}
+
+func TestLandingLinkPermalink(t *testing.T) {
+	th := Setup(t)
+	defer th.TearDown()
+
+	recipient := &model.User{}
+	post := &model.Post{
+		Id:      "Test_id",
+		Message: "This is the message",
+	}
+	channel := &model.Channel{
+		DisplayName: "ChannelName",
+		Type:        model.CHANNEL_OPEN,
+	}
+	channelName := "ChannelName"
+	senderName := "sender"
+	teamName := "team"
+	teamURL := "http://localhost:8065/landing#/" + teamName
+	emailNotificationContentsType := model.EMAIL_NOTIFICATION_CONTENTS_FULL
+	translateFunc := utils.GetUserTranslations("en")
+
+	body := th.App.getNotificationEmailBody(recipient, post, channel, channelName, senderName, teamName, teamURL, emailNotificationContentsType, true, translateFunc)
+	require.Contains(t, body, teamURL+"/pl/"+post.Id, fmt.Sprintf("Expected email text '%s'. Got %s", teamURL, body))
+}