Add route to launch session on student computers with bit.ly link

<!--- Please write your PR name in the present imperative tense.
Examples of that tense are: "Fix issue in the dispatcher where…",
"Improve our handling of…", etc." -->
<!-- For more information on Pull Requests, you can reference here:
https://success.vanillaforums.com/kb/articles/228-using-pull-requests-to-contribute
-->
## Describe Your Changes

- Add route '/games/sessions' that matches available bit.ly link (bit.ly/blueredgame)
- Adjust template to accept session id from instructor
- Use js to manage redirects including older one; previously we used the
standard form with query strings.

## Non-Obvious Technical Information


## Checklist Before Requesting a Review
- [x] The code runs successfully.

```commandline
2023-12-26 12:58:24 INFO:     Application startup complete.
2023-12-26 12:58:31 INFO:     172.25.0.1:40658 - "GET /games/sessions HTTP/1.1" 200 OK
2023-12-26 12:59:36 INFO:     172.25.0.1:53164 - "GET /games/session/4/ HTTP/1.1" 307 Temporary Redirect
2023-12-26 12:59:36 INFO:     172.25.0.1:53164 - "GET /games/session/4 HTTP/1.1" 200 OK
2023-12-26 12:59:38 INFO:     172.25.0.1:53164 - "GET /games/10/player/59/ready HTTP/1.1" 200 OK
```

prijateli_tree/app/routers/games.py

@@ -58,10 +58,18 @@
 ###############################
 
 
+@router.get("/sessions", response_class=HTMLResponse)
+def choose_session_id(request: Request) -> Response:
+    return templates.TemplateResponse(
+        "new_session.html",
+        context={"request": request, "session_id": -1},
+    )
+
+
 @router.get("/session/{session_id}", response_class=HTMLResponse)
-def route_session_access(
+def choose_session_players(
     request: Request, session_id: int, db: Session = Depends(get_db)
-):
+) -> Response:
     games = db.query(Game).filter_by(game_session_id=session_id).all()
     raise_exception_if_not(games, "session not found or games not created")
 
@@ -80,13 +88,13 @@ def route_session_access(
     )
 
 
-@router.get("/{game_id}/ready", response_class=HTMLResponse)
+@router.get("/{game_id}/player/{player_id}/ready", response_class=HTMLResponse)
 def start_session(
     request: Request,
     game_id: int,
     player_id: int,
     db: Session = Depends(get_db),
-):
+) -> Response:
     _, player = get_game_and_player(game_id, player_id, db)
     template_text = languages[player.language.abbr]
 

prijateli_tree/app/templates/new_session.html

@@ -1,19 +1,65 @@
 {% extends "base.html" %}
+{% block helper_script %}
+  <script>
+function redirectToChoosePlayers() {
+  // Get the session ID from the input field
+  const sessionId = document.getElementById("session_id").value;
+
+  // Construct the URL with the session ID
+  const url = "/games/session/" + sessionId + "/";
+
+  // Redirect to the generated URL
+  window.location.href = url;
+}
+
+function redirectToSession() {
+  // Get the session ID from the input field
+  const playerId = document.getElementById("player_id").value;
+  const gameId =  document.getElementById("game_id").value;
+
+  // Construct the URL with the session ID
+  const url = "/games/" + gameId + "/player/" + playerId + "/ready";
+
+  // Redirect to the generated URL
+  window.location.href = url;
+}
+
+  </script>
+{% endblock helper_script %}
 {% block title %}
   PrijateliTree - Access Session
 {% endblock title %}
 {% block content %}
   <div class="container-sm flex-container">
     <h1>Welcome.</h1>
-    <h2>Select the name of the student who will sit at this desk.</h2>
-    <div class="col-sm-4">
-      <form method="get" action='{{ url_for("start_session", game_id=game_id) }}'>
-        <!--<label for="num-games" class="col-sm-4 col-form-label"></label>-->
-        <select id="player_id" class="form-select form-select-sm" name="player_id">
-          {% for p in players %}<option value="{{ p.id }}">{{ p.user.name_str }}</option>{% endfor %}
-        </select>
-        <button type="submit" class="btn btn-primary float-end">Start</button>
-      </form>
-    </div>
+    {% if session_id == -1 %}
+      <p>Enter the session id.</p>
+      <div class="col-sm-4">
+        <form>
+          <input type="text" id="session_id" name="session_id">
+          <br>
+          <br>
+          <button type="button"
+                  onclick="redirectToChoosePlayers()"
+                  class="btn btn-primary float-start">Next</button>
+        </form>
+      </div>
+    {% else %}
+      <p>Select the name of the student who will sit at this desk.</p>
+      <div class="col-sm-4">
+        <form>
+          <input type="text" id="game_id" value={{ game_id }} hidden>
+          <select id="player_id" class="form-select form-select-sm" name="player_id">
+            {% for p in players %}<option value="{{ p.id }}">{{ p.user.name_str }}</option>{% endfor %}
+          </select>
+          <br>
+          <br>
+          <!--<button type="submit" class="btn btn-primary float-start">Start</button>-->
+          <button type="button"
+                  onclick="redirectToSession()"
+                  class="btn btn-primary float-start">Start</button>
+        </form>
+      </div>
+    {% endif %}
   </div>
 {% endblock content %}