Adding frequency_control_specs under AdSet for BrandAwreness

Summary: Modify SDK for Brand Awareness

Test Plan:
All Integration and unit tests pass
ritu-mbp:python-ads-sdk ritu$ python -m facebookads.test.integration
......................
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Ran 22 tests in 24.138s

OK
ritu-mbp:python-ads-sdk ritu$ python -m facebookads.test.unit
.............................
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Ran 29 tests in 0.014s

OK

Author: Rituparna Mukherjee

facebookads/objects.py

@@ -1383,6 +1383,7 @@ class Field(HasBidInfo, object):
         effective_status = 'effective_status'
         end_time = 'end_time'
         execution_options = 'execution_options'
+        frequency_control_specs = 'frequency_control_specs'
         id = 'id'
         is_autobid = 'is_autobid'
         lifetime_budget = 'lifetime_budget'