chore: add Into conversions for Blob to [u8] (#3877)

## Motivation and Context
Often I have a &[u8] or a Vec<u8>, but the sdk function takes a Blob.
It would be convenient to pass the my_vec instead of
aws_smithy_types::Blob::new(my_vec)

## Description
In blob.rs I added
Into<Vec<u8>> for Blob
Into<Blob> for Vec<u8>
Into<Blob> for &[u8]


## Testing
Added a test to blob.rs to test the various scenarios.

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