feat: added service for navigation rpc

[moritzzimmer]

what

1. provide new rpc to retrieve t-online navigation as a tree structure
2. bumped java version to 17

why

align navigation data in our products

example

{
  "navigation_menu": {
    "children": [
      {
        "children": [
          {
            "children": [],
            "fields": {},
            "type": "",
            "label": "Deutschland",
            "href": "/nachrichten/deutschland/"
          },
          {
            "children": [],
            "fields": {},
            "type": "",
            "label": "Ausland",
            "href": "/nachrichten/ausland/"
          },
          {
            "children": [],
            "fields": {},
            "type": "",
            "label": "Corona-Krise",
            "href": "/nachrichten/corona-krise/"
          },
          {
            "children": [],
            "fields": {},
            "type": "",
            "label": "Tagesanbruch",
            "href": "/nachrichten/tagesanbruch/"
          }
        ],
        "fields": {},
        "type": "",
        "label": "Politik",
        "href": "/nachrichten/"
      },
      {
        "children": [],
        "fields": {},
        "type": "",
        "label": "Ukraine",
        "href": "/nachrichten/ukraine/"
      }
    ],
    "fields": {},
    "type": "",
    "label": "navigation_menu",
    "href": "/"
  }
}

[moritzzimmer]

idea: use a new package instead of fragement to make major versions bumps/dependencies easier in the future....

[thisismana]

rpc GetNavigation(google.protobuf.Empty) returns (GetNavigationResponse) {}

and then add a message later if required?

see https://cloud.google.com/java/docs/reference/protobuf/latest/com.google.protobuf.Empty and https://stackoverflow.com/a/51426142/12016

already been used in: core_article_service.proto

A generic empty message that you can re-use to avoid defining duplicated empty messages in your APIs. A typical example is to use it as the request or the response type of an API method. For instance: service Foo { rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty); } The JSON representation for Empty is empty JSON object {}.