Set version of AST in a config file

[james-garriss]

💡 Summary

Currently the version of Azure Sign Tool (AST) that is used for signing is hard-coded in a workflow. It's being moved into a PowerShell version. The version installed should be specified in some sort of config file or constants file.

This is related to epic #1136 and issue #1140.

Motivation and context

This type of information should be found in one file that everyone can see and use.

Implementation notes

This issue should not reinvent the wheel. Whatever solution is created in #1140 should simply be reused here.
The code that installs AST should use the value in the config/constants file.

Acceptance criteria

How do we know when this work is done?

• The version of AST that is installed is no longer hard-coded.