feat(motd): add the ability to use custom style (#2918)

* feat(motd): rework motd display mechanism for more flexibility on motd content

* feat(api): enhance MOTD

* refactor(api): refactor MOTD related codebase

* feat(motd): hash on message

api/http/handler/motd/motd.go

@@ -1,7 +1,9 @@
 package motd
 
 import (
+	"encoding/json"
 	"net/http"
+	"strings"
 
 	"github.com/portainer/libhttp/response"
 	"github.com/portainer/portainer/api"
@@ -10,25 +12,44 @@ import (
 )
 
 type motdResponse struct {
-	Title   string `json:"Title"`
-	Message string `json:"Message"`
-	Hash    []byte `json:"Hash"`
+	Title         string            `json:"Title"`
+	Message       string            `json:"Message"`
+	ContentLayout map[string]string `json:"ContentLayout"`
+	Style         string            `json:"Style"`
+	Hash          []byte            `json:"Hash"`
+}
+
+type motdData struct {
+	Title         string            `json:"title"`
+	Message       []string          `json:"message"`
+	ContentLayout map[string]string `json:"contentLayout"`
+	Style         string            `json:"style"`
 }
 
 func (handler *Handler) motd(w http.ResponseWriter, r *http.Request) {
-
 	motd, err := client.Get(portainer.MessageOfTheDayURL, 0)
 	if err != nil {
 		response.JSON(w, &motdResponse{Message: ""})
 		return
 	}
 
-	title, err := client.Get(portainer.MessageOfTheDayTitleURL, 0)
+	var data motdData
+	err = json.Unmarshal(motd, &data)
 	if err != nil {
 		response.JSON(w, &motdResponse{Message: ""})
 		return
 	}
 
-	hash := crypto.HashFromBytes(motd)
-	response.JSON(w, &motdResponse{Title: string(title), Message: string(motd), Hash: hash})
+	message := strings.Join(data.Message, "\n")
+
+	hash := crypto.HashFromBytes([]byte(message))
+	resp := motdResponse{
+		Title:         data.Title,
+		Message:       message,
+		Hash:          hash,
+		ContentLayout: data.ContentLayout,
+		Style:         data.Style,
+	}
+
+	response.JSON(w, &resp)
 }