[SQL] Add Swagger and examples for ManagedDatabases

[AutorestCI]

Generated from RestAPI PR: Azure/azure-rest-api-specs#1812

[lmazuel]

LGTM

[jaredmoo]

ManagedDatabases isn't in production yet, I am removing this from the readme in Azure/azure-rest-api-specs#1949

[codecov-io]

Codecov Report

Merging #1586 into master will decrease coverage by 0.06%.
The diff coverage is 26.54%.

@@            Coverage Diff             @@
##           master    #1586      +/-   ##
==========================================
- Coverage   53.82%   53.76%   -0.07%     
==========================================
  Files        3675     3680       +5     
  Lines       90911    91122     +211     
==========================================
+ Hits        48932    48988      +56     
- Misses      41979    42134     +155

Impacted Files	Coverage Δ
azure-mgmt-sql/azure/mgmt/sql/models/__init__.py	100% <100%> (ø)	⬆️
...e-mgmt-sql/azure/mgmt/sql/sql_management_client.py	100% <100%> (ø)	⬆️
...ure/mgmt/sql/models/sql_management_client_enums.py	100% <100%> (ø)	⬆️
...ure-mgmt-sql/azure/mgmt/sql/operations/__init__.py	100% <100%> (ø)	⬆️
...gmt/sql/operations/managed_databases_operations.py	11.48% <11.48%> (ø)
...mgmt-sql/azure/mgmt/sql/models/managed_database.py	31.25% <31.25%> (ø)
...l/azure/mgmt/sql/models/managed_database_update.py	31.25% <31.25%> (ø)
...ql/azure/mgmt/sql/models/managed_database_paged.py	80% <80%> (ø)
...ls/complete_managed_database_restore_definition.py	83.33% <83.33%> (ø)
... and 4 more

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[lmazuel]

Close, since not in production yet.