async CredentialProvider

[yulin-li]

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Description of change

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This a draft PR to explain #3422

The PR introduces breaking changes and we may need to update it to make it backward compatible.

[vladvildanov]

@yulin-li I suggest to extend an existing interface with smth like get_credentials_async() to make it backward compatible. I'm planning to do this as a part of #3423

[yulin-li]

that would be great!