Onlap example for video tutorials (#1030)

# Description
Uploaded the new onlap example for the video tutorial series.

Relates to <issue>

# Checklist
- [x] My code uses type hinting for function and method arguments and return values.
- [x] I have created tests which cover my code.
- [x] The test code either 1. demonstrates at least one valuable use case (e.g. integration tests) 
or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
- [x] New tests pass locally with my changes.

Author: Leguark

examples/tutorials/z_other_tutorials/video_tutorial_model_3_onlap.py

@@ -0,0 +1,214 @@
+"""
+Video Tutorial "code-along": Onlap relations
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+"""
+
+
+# %%
+# This tutorial demonstrates step-by-step how to incorporate onlap relations to our geological models created with gempy.
+# It follows the Video tutorial series available on the [gempy YouTube channel](https://www.youtube.com/@GemPy3D).
+# Please follow the first and second part of the tutorials to learn the basics of modeling with gempy before diving into this tutorial.
+
+# %%
+# Video tutorial 11: Basic onlap scenario
+# """"""""""""""""""""""""""""""""""""
+
+
+# %%
+# .. raw:: html
+#
+#     <iframe width="560" height="315"
+#             src="https://www.youtube.com/embed/80QjnrFxubQ"
+#             title="YouTube video player"
+#             frameborder="0"
+#             allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
+#             allowfullscreen>
+#     </iframe>
+#
+#
+
+# %%
+
+# Required imports
+import gempy as gp
+import gempy_viewer as gpv
+import numpy as np
+
+# %%
+
+# Path to input data
+data_path = "https://raw.githubusercontent.com/cgre-aachen/gempy_data/master/"
+path_to_data = data_path + "/data/input_data/video_tutorials_v3/"
+
+# %%
+
+# Create instance of geomodel
+geo_model_onlap = gp.create_geomodel(
+    project_name = 'tutorial_model_onlap_1',
+    extent=[0,2000,0,1000,0,1000],
+    resolution=[100,50,50],
+    importer_helper=gp.data.ImporterHelper(
+        path_to_orientations=path_to_data+"tutorial_model_onlap_1_orientations.csv",
+        path_to_surface_points=path_to_data+"tutorial_model_onlap_1_surface_points.csv"
+    )
+)
+
+
+# %%
+
+# Map geological series to surfaces
+gp.map_stack_to_surfaces(
+    gempy_model=geo_model_onlap,
+    mapping_object={
+        "Young_Series": ("basin_fill_2", "basin_fill_1"),
+        "Old_Series": ("basin_top", "basin_bottom")
+    }
+)
+
+# Alternative way of mapping geological series to surfaces
+# gp.map_stack_to_surfaces(
+#     gempy_model=geo_model_onlap,
+#     mapping_object={
+#         "Young_Series": ("basin_fill_2", "basin_fill_1"),
+#         "Onlap_Series": ("basin_top"),
+#         "Old_Series": ("basin_bottom")
+#     }
+# )
+
+# %%
+
+# Display a basic cross section of input data
+gpv.plot_2d(geo_model_onlap, show_data=True)
+
+# %%
+
+# Compute a solution for the model
+gp.compute_model(geo_model_onlap)
+
+# %%
+
+# Display the result in 2d section
+gpv.plot_2d(geo_model_onlap, show_boundaries=False)
+
+# %%
+
+# Set the relation of the youngest group to Onlap
+from gempy_engine.core.data.stack_relation_type import StackRelationType
+geo_model_onlap.structural_frame.structural_groups[0].structural_relation = StackRelationType.ONLAP
+
+# %%
+
+# Display updated strucutral frame
+geo_model_onlap.structural_frame
+
+# %%
+
+# Compute a solution for the model
+gp.compute_model(geo_model_onlap)
+
+# %%
+
+# Display the result in 2d section
+gpv.plot_2d(geo_model_onlap, show_boundaries=False)
+
+# %%
+# Video tutorial 12: Advanced onlap - Subduction zone
+# """"""""""""""""""""""""""""
+
+# %%
+# .. raw:: html
+#
+#     <iframe width="560" height="315"
+#             src="https://www.youtube.com/embed/R-vUld4V-OQ"
+#             title="YouTube video player"
+#             frameborder="0"
+#             allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
+#             allowfullscreen>
+#     </iframe>
+#
+#
+
+# %%
+
+# Create instance of geomodel
+geo_model_subduction = gp.create_geomodel(
+    project_name = 'tutorial_model_onlap_2',
+    extent=[0,2000,0,1000,0,1000],
+    resolution=[100,50,50],
+    importer_helper=gp.data.ImporterHelper(
+        path_to_orientations=path_to_data+"tutorial_model_onlap_2_orientations.csv?",
+        path_to_surface_points=path_to_data+"tutorial_model_onlap_2_surface_points.csv?"
+    )
+)
+
+# %%
+
+# Display a basic cross section of input data
+gpv.plot_2d(geo_model_subduction)
+
+# %%
+
+# Map geological series to surfaces
+gp.map_stack_to_surfaces(
+    gempy_model=geo_model_subduction,
+    mapping_object={
+        "Top": ("continental_top"),
+        "Continental_Series": ("continental_shallow", "continental_deep"),
+        "Oceanic_Series": ("oceanic_top", "oceanic_bottom")
+    }
+)
+
+# %%
+
+# Set the realtion of the youngest and second youngest group to Onlap
+geo_model_subduction.structural_frame.structural_groups[0].structural_relation = StackRelationType.ONLAP
+geo_model_subduction.structural_frame.structural_groups[1].structural_relation = StackRelationType.ONLAP
+
+# %%
+
+# Display updated structural frame
+geo_model_subduction.structural_frame
+
+# %%
+
+# Create a simple topography using numpy
+
+# Define grid spacing
+spacing = 20
+
+# Generate grid
+x = np.arange(geo_model_subduction.grid.regular_grid.extent[0], geo_model_subduction.grid.regular_grid.extent[1] + spacing, spacing)
+y = np.arange(geo_model_subduction.grid.regular_grid.extent[2], geo_model_subduction.grid.regular_grid.extent[3] + spacing, spacing)
+X, Y = np.meshgrid(x, y)
+
+# Define elevation (z) based on x, creating a simple mountain range
+Z = np.ones_like(X) * 590  # Default elevation
+Z[(X >= 570) & (X < 1000)] = 590 + (200 * (X[(X >= 570) & (X < 1000)] - 600) / 400)
+Z[(X >= 1000) & (X < 1300)] = 810 - (250 * (X[(X >= 1000) & (X < 1300)] - 1000) / 300)
+Z[X >= 1300] = 540
+
+# Flatten the data into (N,3) shape
+topography_points = np.vstack((X.ravel(), Y.ravel(), Z.ravel())).T
+
+# %%
+
+# Set topography from numpy array
+gp.set_topography_from_arrays(grid=geo_model_subduction.grid, xyz_vertices=topography_points)
+
+# %%
+
+# Compute a solution for the model
+gp.compute_model(geo_model_subduction)
+
+# %%
+
+# Display the result in 2d section
+gpv.plot_2d(geo_model_subduction, show_topography=True, show_boundaries=False)
+
+# %%
+
+# Display 3d plot of final model
+gpv.plot_3d(geo_model_subduction, show_topography=True, image=True)
+
+# sphinx_gallery_thumbnail_number = -1
+