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

[motus]

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Make AzureFlieShareService 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