Add synthetics private location endpoints

[api-clients-generation-pipeline]

See DataDog/datadog-api-spec#674

[jirikuncar]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Merging #584 (7cdecae) into master (9cf6ee7) will increase coverage by 0.02%.
The diff coverage is 37.46%.

Impacted Files	Coverage Δ
...te_location_creation_response_result_encryption.go	0.00% <0.00%> (ø)
...tadog/model_synthetics_private_location_secrets.go	0.00% <0.00%> (ø)
...thetics_private_location_secrets_authentication.go	0.00% <0.00%> (ø)
...tics_private_location_secrets_config_decryption.go	0.00% <0.00%> (ø)
...l_synthetics_private_location_creation_response.go	1.81% <1.81%> (ø)
...pi/v1/datadog/model_synthetics_private_location.go	13.33% <13.33%> (ø)
api/v1/datadog/api_synthetics.go	60.84% <64.58%> (-0.45%)	⬇️
... and 4 more