erp5_hr_calendar: Add PublicHoliday_init PythonScript

It is defined in Portal Type and projects do use versions of it.
Add it as empty in generic implementation, since otherwise the portal type
is unusable (cannot create new documents)

bt5/erp5_hr_calendar/SkinTemplateItem/portal_skins/erp5_hr_calendar/PublicHoliday_init.py

+'''
+  Nothing to do. Script exists to be easily customisable in project
+'''

bt5/erp5_hr_calendar/SkinTemplateItem/portal_skins/erp5_hr_calendar/PublicHoliday_init.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="PythonScript" module="Products.PythonScripts.PythonScript"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>Script_magic</string> </key>
+            <value> <int>3</int> </value>
+        </item>
+        <item>
+            <key> <string>_bind_names</string> </key>
+            <value>
+              <object>
+                <klass>
+                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
+                </klass>
+                <tuple/>
+                <state>
+                  <dictionary>
+                    <item>
+                        <key> <string>_asgns</string> </key>
+                        <value>
+                          <dictionary>
+                            <item>
+                                <key> <string>name_container</string> </key>
+                                <value> <string>container</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_context</string> </key>
+                                <value> <string>context</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_m_self</string> </key>
+                                <value> <string>script</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_subpath</string> </key>
+                                <value> <string>traverse_subpath</string> </value>
+                            </item>
+                          </dictionary>
+                        </value>
+                    </item>
+                  </dictionary>
+                </state>
+              </object>
+            </value>
+        </item>
+        <item>
+            <key> <string>_params</string> </key>
+            <value> <string>*args, **kw</string> </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>PublicHoliday_init</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>