[Storage] [STG 98] Added support for x-ms-file-request-intent for Blob Copy APIs

[weirongw23-msft]

This PR contains the following changes:

1. Created helper functions (sync and async) to manage bearer token credential strings, refactored some existing code to match this pattern
2. Created helper functions to manage creating source files with OAuth
3. Added azure-storage-file-share>=12.20.1 to dev_requirements.txt, the latest GA File Share release, for testing compatibility
4. Added kwargs for source_token_intent to send x-ms-file-request-intent and the appropriate validation for async copy (which is not a part of the feature)
5. Misc. fixes like moving closing parentheses to a new line

As of the first iteration, only the upload_blob_from_url tests has been recorded to check if dev_requirements.txt dependency is scaffolded properly. In addition, I've grouped append_block_from_url tests with test_block_blob.py and test_block_blob_async.py because they're all block blobs to reduce code duplication. I'm open to moving this to test_append_blob.py and test_append_blob_async.py respectively, after the naming, features, and testing structures have been reviewed. Thanks!

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-storage-blob

[jalauzon-msft]

Looks good. Some minor comments on tests.

[weirongw23-msft]

/azp run python - pullrequest

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[vincenttran-msft]