Move away from 'crypto/sha1' for AWS Sign Requests

[davissp14]

SHA1 has been deemed unsafe for a while now. The use of HMAC-SHA1 is a little better, we should look to move to SHA2 or SHA3 for better security.

Describe the solution you'd like
Move to SHA2 or SHA3

https://github.ibm.com/ibm-cloud-databases/velero/blob/6513e8f30e8314f2188159b3472fd627a9bd2619/pkg/cloudprovider/aws/v1_sign_request_handler.go#L21

[skriss]

@davissp14 the v1 signature handler you're referencing is not the default. #998 will give you some more context on why that exists. v4 is used by default.

[skriss]

Closing this out as the default signing method is v4 which uses SHA-2, and the v1 handler is around for backwards compatibility for other providers and is opt-in only.