[SQL] Add list apis for sql backup LTR policies & vaults

[AutorestCI]

Generated from RestAPI PR: Azure/azure-rest-api-specs#2006

[codecov-io]

Codecov Report

Merging #1634 into master will decrease coverage by 0.03%.
The diff coverage is 25.22%.

@@            Coverage Diff             @@
##           master    #1634      +/-   ##
==========================================
- Coverage   56.08%   56.05%   -0.04%     
==========================================
  Files        3902     3905       +3     
  Lines       94287    94380      +93     
==========================================
+ Hits        52881    52903      +22     
- Misses      41406    41477      +71

Impacted Files	Coverage Δ
azure-mgmt-sql/azure/mgmt/sql/models/__init__.py	100% <100%> (ø)	⬆️
azure-mgmt-sql/azure/mgmt/sql/version.py	100% <100%> (ø)	⬆️
.../azure/mgmt/sql/operations/databases_operations.py	27.56% <18.36%> (-1.32%)	⬇️
...ns/backup_long_term_retention_vaults_operations.py	19.75% <4.76%> (-5.25%)	⬇️
.../backup_long_term_retention_policies_operations.py	19.75% <4.76%> (-5.25%)	⬇️
...l/models/backup_long_term_retention_vault_paged.py	80% <80%> (ø)
.../models/backup_long_term_retention_policy_paged.py	80% <80%> (ø)
.../azure/mgmt/sql/models/resource_move_definition.py	83.33% <83.33%> (ø)
... and 1 more

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[lmazuel]

See #1718