update-dependencies can only access publicly available .NET checksums/shas

[lbussell]

Related:

• Redesign update-dependencies tool to better support internal builds #6305
• Add staging pipeline support to update-dependencies tool #6473

The dependency update code for acquiring checksums should be refactored so that it can use the checksum files from the staging storage account.

Thanks to #6473, we can now use a service connection to access the staging storage account. However, the code in SpecificCommand (which does the checksum updates/calculation) has no knowledge of the storage account yet.

This does not affect releases because .NET checksums are publicly available several days before a release goes live. This mostly impacts release validation and staging because those need to happen before the release is finalized.