feat: add "id" column to Titanic dataset (#29)

### Summary of Changes

Names alone were not unique, so I've added an "id" column.

docs/examples/titanic.ipynb

@@ -116,12 +116,16 @@
    "execution_count": null,
    "outputs": [],
    "source": [
-    "from safeds.data.tabular import Table\n",
     "from safeds.plotting import correlation_heatmap\n",
     "\n",
-    "titanic_correlation = Table.from_columns(\n",
-    "    titanic.list_columns_with_numerical_values()\n",
-    ")\n",
+    "titanic_correlation = titanic.keep_columns([\n",
+    "    \"age\",\n",
+    "    \"siblings_spouses\",\n",
+    "    \"parents_children\",\n",
+    "    \"travel_class\",\n",
+    "    \"fare\",\n",
+    "    \"survived\"\n",
+    "])\n",
     "correlation_heatmap(titanic_correlation)"
    ],
    "metadata": {

src/safeds_examples/tabular/_titanic/_titanic.py

@@ -31,6 +31,7 @@ def describe_titanic_columns() -> Table:
 
     return Table(
         [
+            {"Name": "id", "Description": "A unique identifier"},
             {"Name": "name", "Description": "Name of the passenger"},
             {"Name": "sex", "Description": "Sex of the passenger"},
             {"Name": "age", "Description": "Age of the passenger at the time of the accident"},