[FIX] base: allow server actions to en/decode base64

This is usefull when dealing with binary fields.
This was possible in previous versions in python 2 using
`str.encode('base64')`.

odoo/addons/base/ir/ir_actions.py

@@ -8,6 +8,7 @@ from odoo.tools.safe_eval import safe_eval, test_python_expr
 from odoo.tools import pycompat
 from odoo.http import request
 
+import base64
 from collections import defaultdict
 import datetime
 import dateutil
@@ -76,6 +77,8 @@ class IrActions(models.Model):
             'datetime': datetime,
             'dateutil': dateutil,
             'timezone': timezone,
+            'b64encode': base64.b64encode,
+            'b64decode': base64.b64decode,
         }
 
     @api.model