Adding VA support for manged instance

[yaakoviyun]

Adding Vulnerability Assessment APIs on managed instance

Those APIs are the same as the Vulnerability Assessment APIs on regular Azure db with the difference of using "/managedInstances/{managed instance name}/" instead of "/servers/{server name}/"

The Vulnerability Assessment APIs on regular Azure db are approved and can be found at:

https://github.com/Azure/azure-rest-api-specs/blob/master/specification/sql/resource-manager/Microsoft.Sql/preview/2017-03-01-preview/databaseVulnerabilityAssessmentBaselines.json

https://github.com/Azure/azure-rest-api-specs/blob/master/specification/sql/resource-manager/Microsoft.Sql/preview/2017-03-01-preview/databaseVulnerabilityAssessments.json

https://github.com/Azure/azure-rest-api-specs/blob/master/specification/sql/resource-manager/Microsoft.Sql/preview/2017-10-01-preview/databaseVulnerabilityAssessmentScans.json

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[AutorestCI]

Automation for azure-sdk-for-python

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-python#2671

[AutorestCI]

Automation for azure-sdk-for-java

Nothing to generate for azure-sdk-for-java

[AutorestCI]

Automation for azure-sdk-for-ruby

Nothing to generate for azure-sdk-for-ruby

[yaakoviyun]

@jaredmoo for reference

[AutorestCI]

Automation for azure-sdk-for-go

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-go#2435

[AutorestCI]

Automation for azure-sdk-for-node

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-node#3293

[yaakoviyun]

@sarangan12 - can we get someone from ARM to review the API?

[sarangan12]

@ravbhatnagar Can you please review this from ARM side and provide your signoff?

[sarangan12]

@ravbhatnagar Did you get a chance to review this?

[yaakoviyun]

@sarangan12 - can you help.
This PR is waiting for a long time...

[azuresdkci]

Can one of the admins verify this patch?

[yaakoviyun]

@sarangan12 - can you help?

[yaakoviyun]

Ping...

[jhendrixMSFT]

@AutorestCI regenerate azure-sdk-for-go

[yaakoviyun]

@sarangan12 - can you merge the PR.