Change CI to GitHub actions

Use copier template from oca/oca-addons-repo-template

Target Python3.7

Adapt modules to fix few issues

attachment_s3/__manifest__.py

@@ -12,7 +12,7 @@
  'external_dependencies': {
      'python': ['boto3'],
  },
- 'website': 'https://www.camptocamp.com',
+ 'website': 'https://github.com/camptocamp/odoo-cloud-platform',
  'data': [],
  'installable': True,
  }

attachment_s3/models/ir_attachment.py

@@ -39,9 +39,9 @@ class IrAttachment(models.Model):
     _inherit = "ir.attachment"
 
     def _get_stores(self):
-        l = ['s3']
-        l += super(IrAttachment, self)._get_stores()
-        return l
+        stores = ['s3']
+        stores += super(IrAttachment, self)._get_stores()
+        return stores
 
     @api.model
     def _get_s3_connection_params(self, bucket_name=None):