Do not show __init__ method in document

docs/_templates/autosummary/class.rst

@@ -0,0 +1,20 @@
+{% extends "!autosummary/class.rst" %}
+
+{#
+Ref: https://github.com/optuna/optuna/blob/41045cef7a8f5d0e5e4026bf0c5c649b269fc312/docs/source/_templates/autosummary/class.rst
+An autosummary template to exclude the class constructor (__init__)
+which doesn't contain any docstring in Optuna Dashboard.
+#}
+
+{% block methods %}
+   {% set methods = methods | select("ne", "__init__") | list %}
+   {% if methods %}
+   .. rubric:: Methods
+
+   .. autosummary::
+   {% for item in methods %}
+      ~{{ name }}.{{ item }}
+   {%- endfor %}
+   {% endif %}
+
+{% endblock %}