Use token-based authentication instead of the access key in the AzureFileShareService

[motus]

Make AzureFileShareService class use token-based credential instead of the access key. This PR is part of #777

NOTE:

• We have to use late initialization of the _share_client to avoid issues with JSON schema validation tests.
• More PRs will follow:
  • Use to azcopy on the remote VMs instead of mounting the file share using the access key
  • Remove references to "storageAccountKey" from configurations and tests and document the new mechanism

[bpkroth]

Part of why we went with the mount smb method was reduced dependencies on the target VM.

Use of azcopy instead might be a little more challenging on that front, but let's see.

[bpkroth]

As long as we're removing account storage key, does removing fileshare also make sense? We could use blobs instead I guess. Maybe less nice though and too many changes.

[bpkroth]

Mostly looks good. Only feedback was to move the SupportsAuth check to __init__ so we can check for proper configs at startup time rather than at file transfer need time which might be after some experiment trial has already run.