Adds auto object store creation to get_file

[dakinggg]

What does this PR do?

I have had to write code that autoparses the URI to create an S3ObjectStore and then calls get_file with that newly created object store a couple of times, and the util to pull huggingface tokenizer/model out of a composer checkpoint is going to need to do the same, so I added the same auto parsing support as in trainer to the get_file function. It shouldn't change any behavior of any existing code interacting with get_file.

Manual tested that I can download a file from S3 using this, and also that checkpointing/autoresume from S3 still works.

What issue(s) does this change relate to?

Part of CO-1110

Before submitting

• Have you read the contributor guidelines?
• Is this change a documentation change or typo fix? If so, skip the rest of this checklist.
• Was this change discussed/approved in a GitHub issue first? It is much more likely to be merged if so.
• Did you update any related docs and document your change?
• Did you update any related tests and add any new tests related to your change? (see testing)
• Did you run the tests locally to make sure they pass?
• Did you run pre-commit on your change? (see the pre-commit section of prerequisites)

[eracah]

Nice LGTM. Maybe at some point we can push ALL the auto-parsing logic to get_file and to upload_file