Add LoadBalancer features

[dingmeng-xue]

Description

• Updated below cmdlet
  -New-AzLoadBalancerFrontendIpConfigCommand, Set-AzLoadBalancerFrontendIpConfigCommand, Add-AzLoadBalancerFrontendIpConfigCommand:
  - Added PublicIpAddressPrefix property
  - Added PublicIpAddressPrefixId property
• Added new properties to the following cmdlets to allow for global load balancing
  • New-AzLoadBalancer:
    • Added Sku Tier property
  • New-AzPuplicIpAddress:
    • Added Sku Tier property
  • New-AzPublicIpPrefix:
    • Added Sku Tier property
  • New-AzLoadBalancerBackendAddressConfig:
    • Added LoadBalancerFrontendIPConfigurationId property

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• 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:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
    • {Please put the link here}
  • the markdown help files have been regenerated using the commands listed here