[Datafactory] Adding additionProperties to allow serializing/deserializing new properties as JSON extension data

[AutorestCI]

Generated from RestAPI PR: Azure/azure-rest-api-specs#2033

[codecov-io]

Codecov Report

Merging #1640 into master will increase coverage by <.01%.
The diff coverage is 57.25%.

@@            Coverage Diff             @@
##           master    #1640      +/-   ##
==========================================
+ Coverage   56.13%   56.13%   +<.01%     
==========================================
  Files        3956     4045      +89     
  Lines       94940    95966    +1026     
==========================================
+ Hits        53296    53872     +576     
- Misses      41644    42094     +450

Impacted Files	Coverage Δ
...tory/operations/integration_runtimes_operations.py	38.18% <0%> (ø)	⬆️
...y/azure/mgmt/datafactory/models/lookup_activity.py	100% <100%> (ø)	⬆️
...tafactory/azure/mgmt/datafactory/models/factory.py	100% <100%> (ø)	⬆️
...tory/azure/mgmt/datafactory/models/activity_run.py	100% <100%> (ø)	⬆️
...tafactory/azure/mgmt/datafactory/models/dataset.py	100% <100%> (ø)	⬆️
...zure/mgmt/datafactory/models/azure_blob_dataset.py	100% <100%> (ø)	⬆️
...afactory/models/self_hosted_integration_runtime.py	100% <100%> (ø)	⬆️
...ctory/azure/mgmt/datafactory/models/copy_source.py	100% <100%> (ø)	⬆️
...y/models/self_hosted_integration_runtime_status.py	100% <100%> (ø)	⬆️
...e/mgmt/datafactory/models/get_metadata_activity.py	100% <100%> (ø)	⬆️
... and 328 more

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[lmazuel]

Released as 0.3.0 part of another PR