Add support for ApiVersionSetId in Import and add overloads for GetSubscriptions

[solankisamir]

Description

• Fix for issue Get-AzureRmApiManagementSubscription ByProductAndUser #8671

  • Get-AzApiManagementSubscription
    • Added support for querying subscriptions by User and Product
    • Added support for querying using Scope "/", "/apis", "/apis/echo-api"

• Fix for issue request: Import-AzureManagementApi to support api version parameter #9307 and Import-AzureRmApiManagementApi can not set version #8432

  • Import-AzApiManagementApi
    • Added support for specifiying ApiVersion and ApiVersionSetId when importing Apis

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate change log has been updated
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • the changes have gone through a cmdlet design review (Microsoft internal partners only)
  • the cmdlet markdown files were generated using the platyPS module

[cormacpayne]

@solankisamir one small comment, otherwise LGTM

[cormacpayne]

@solankisamir this parameter should be mandatory to avoid any possible conflicts with the GetAllSubscriptions parameter set -- you'll also want to regenerate the help for this cmdlet after making this change

[solankisamir]

fixed