Add pipeline step that requires shared code to match

[mccoyp]

Some libraries -- like Key Vault, Service Bus, and Storage -- use shared code across packages that should always be kept in sync (in KV and Storage, these are _shared folders by convention). We should use automation to ensure this synchronization is actually maintained.

@kashifkhan wrote up a bash script that accepts a list of folders and checks that each folder contains the exact same contents. We should plug this into pipeline(s) where necessary to ensure library owners are 1. aware of misalignment; and 2. blocked from releasing packages that are misaligned.

Since synchronization is usually done by just copy/pasting the code that needs to be shared, misalignments can be quickly resolved. Nightly checks (that also run during release pipelines) therefore seem appropriate for raising the error without being an outsize burden on success metrics.

[annatisch]

Thanks @mccoyp - please also add this to the Communications packages (also using the _shared convention).