Add serde_json for EBS
Add serde_json for EBS

The StartSnapshot API requires it.

Signed-off-by: Ben Cressey <d5f18238126819ea7886c918c0d8abfbd00c3032@amazon.com>

DualSpark/rust-aws,rusoto/rusoto,DualSpark/rusoto,DualSpark/rust-aws,DualSpark/rust-aws,rusoto/rusoto,rusoto/rusoto,DualSpark/rusoto,DualSpark/rusoto