BlobStorage: Possibility of downloading a batch of blobs

### Which service(blob, file, queue) does this issue concern?
blob

### Which version of the SDK was used? Please provide the output of `pip freeze`.
azure-storage-blob==1.4.0
azure-storage-common==1.4.0

### What problem was encountered?
I am missing the possibility of downloading/reading a batch of blobs (specifically a "folder") -- a functionality which is already present in the Azure CLI (`az storage blob download-batch`). I am currently using the `service.get_blob_to_text(container: str, path: str)`, and I imagine the syntax being `service.get_blobs_to_text(container: str, paths: iterable)`.

### Have you found a mitigation/solution?
Currently I am reading the files one-by-one, which generates a performance overhead.

Start from the existing service.get_blob_to_text(container, path) entry point and compare its behavior with the Azure CLI's az storage blob download-batch command. Define how a batch of paths or a folder should be read and what reduced request overhead means for completion; the issue does not name implementation files or tests.

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