Ui-menu: add configurable option for opfab-theme parameter name and values

[quinarygio]

Today Opfab adds a "opfab-theme" parameter to menu url configured in ui-menu.json Make theme parameter name and values configurable. If not specified it will keep the default "opfab-theme" parameter name with "DAY" and "NIGTH" values. Example:

{
      "id": "menu2",
      "entries": [
        {
          "customMenuId": "uid_test_1",
          "url": "https://opfab.github.io/",
          "label": "menu2.entry.single",
          "linkType": "BOTH",
          "dayNightTheme": {
            "attribute": "theme",
            "day": "light",
            "night": "dark" 
          }
        }
      ]
    }