(azcopy) Fix script to handle URL redirection in PowerShell Core

[robmoss2k]

Description

The script fails in PowerShell Core because of the change to how redirects are handled by Invoke-WebRequest. This change uses System.Net objects to avoid this behaviour.

Motivation and Context

Fix the script to work in PowerShell Core.

How Has this Been Tested?

Executed update.ps1 locally.

Screenshot (if appropriate, usually isn't needed):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Migrated package (a package has been migrated from another repository)

Checklist:

• My code follows the code style of this repository.
• My change requires a change to documentation (this usually means the notes in the description of a package).
• I have updated the documentation accordingly (this usually means the notes in the description of a package).
• I have updated the package description and it is less than 4000 characters.
• All files are up to date with the latest Contributing Guidelines
• The added/modified package passed install/uninstall in the Chocolatey Test Environment(https://github.com/chocolatey-community/chocolatey-test-environment/). Note that we don't support the use of any other environment.
• The changes only affect a single package (not including meta package).

[AppVeyorBot]

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[AppVeyorBot]

✅ Package verification completed without issues. PR is now pending human review