Enable IMDSv1 fallback for retrieving credentials from instance metadata.

[jackye1995]

Useful for feature parity with Arrow object_store: https://github.com/apache/arrow-rs-object-store/blob/main/src/aws/builder.rs#L141-L142

[Xuanwo]

This issue is ready to be implemented at https://github.com/apache/opendal-reqsign/blob/main/services/aws-v4/src/provide_credential/imds.rs

Do you have interest to work on this?

[jackye1995]

sounds good!