Automatize Tutorials html, py files creation (#496)

* workflow to export tutorials

---------

tutorials/tutorial6/tutorial.ipynb

@@ -26,21 +26,30 @@
    "source": [
     "## routine needed to run the notebook on Google Colab\n",
     "try:\n",
-    "  import google.colab\n",
-    "  IN_COLAB = True\n",
+    "    import google.colab\n",
+    "\n",
+    "    IN_COLAB = True\n",
     "except:\n",
-    "  IN_COLAB = False\n",
+    "    IN_COLAB = False\n",
     "if IN_COLAB:\n",
-    "  !pip install \"pina-mathlab\"\n",
+    "    !pip install \"pina-mathlab\"\n",
     "\n",
     "import matplotlib.pyplot as plt\n",
     "\n",
-    "from pina.domain import EllipsoidDomain, Difference, CartesianDomain, Union, SimplexDomain, DomainInterface\n",
+    "from pina.domain import (\n",
+    "    EllipsoidDomain,\n",
+    "    Difference,\n",
+    "    CartesianDomain,\n",
+    "    Union,\n",
+    "    SimplexDomain,\n",
+    "    DomainInterface,\n",
+    ")\n",
     "from pina.label_tensor import LabelTensor\n",
     "\n",
+    "\n",
     "def plot_scatter(ax, pts, title):\n",
     "    ax.title.set_text(title)\n",
-    "    ax.scatter(pts.extract('x'), pts.extract('y'), color='blue', alpha=0.5)"
+    "    ax.scatter(pts.extract(\"x\"), pts.extract(\"y\"), color=\"blue\", alpha=0.5)"
    ]
   },
   {