implement pool group and user get routes,

improvements to http return codes,
add localdb backend handler

app/localdb/localdb.go

@@ -0,0 +1,46 @@
+package localdb
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	common "user-manager-api/app/common"
+)
+
+type DB struct {
+	data map[string]common.Pool
+}
+
+func LoadDB(localDBPath string) (DB, error) {
+	db := DB{}
+	content, err := os.ReadFile(localDBPath)
+	if err != nil {
+		//log.Fatal("Error when opening file: ", err)
+		return db, err
+	}
+	err = json.Unmarshal(content, &db.data)
+	if err != nil {
+		//log.Fatal("Error during Unmarshal(): ", err)
+		return db, err
+	}
+	return db, nil
+}
+
+func SaveDB(localDBPath string, db DB) error {
+	json, err := json.Marshal(db.data)
+	if err != nil {
+		return err
+	}
+	err = os.WriteFile(localDBPath, []byte(json), 0644)
+	return err
+}
+
+func (localdb DB) GetPool(poolname string) (common.Pool, []string, int, error) {
+	pool := common.Pool{}
+	pool, ok := localdb.data[poolname]
+	if !ok {
+		return pool, []string{}, http.StatusNotFound, fmt.Errorf("Pool %s not in localdb", poolname)
+	}
+	return pool, []string{}, http.StatusOK, nil
+}