[ADD] create dav_calendar_sync addon

creates new addon dav_calendar_sync to synchronize caldav events on Odoo calendar

dav_calendar_sync/models/calendar_event.py

@@ -0,0 +1,8 @@
+from odoo import _, api, fields, models
+
+
+class Meeting(models.Model):
+    _inherit = 'calendar.event'
+
+    dav_calendar_id = fields.Many2one('dav.calendar', string='Dav Calendar')
+    dav_uid = fields.Char('Dav Uid', index=True)