Initial implementation with AWS SDK for Go v2

[gdavison]

Initial work on using AWS SDK for Go v2 instead of v1.

Authentication is incomplete:

• EC2 instance metadata does not work
• Setting AWS_PROFILE with default shared credentials file does not work
• Directly setting AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY does work

Note: when using this module, you will need to add the following to your go.mod file:

replace github.com/aws/aws-sdk-go-v2/credentials => github.com/gdavison/aws-sdk-go-v2/credentials v1.2.2-0.20210811194025-146c1ad6c3b2

[gdavison]

Hmm, cannot reproduce the go mod check failure

[ewbankkit]

LGTM 🚀.

% make test
go test -timeout=30s -parallel=4 ./...
go: downloading github.com/aws/aws-sdk-go-v2 v1.8.0
go: downloading github.com/aws/aws-sdk-go-v2/config v1.6.0
go: downloading github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.4.0
go: downloading github.com/aws/aws-sdk-go-v2/service/sts v1.6.1
go: downloading github.com/gdavison/aws-sdk-go-v2/credentials v1.2.2-0.20210811194025-146c1ad6c3b2
go: downloading github.com/aws/smithy-go v1.7.0
go: downloading github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.2.2
go: downloading github.com/aws/aws-sdk-go-v2/internal/ini v1.2.0
go: downloading github.com/aws/aws-sdk-go-v2/service/sso v1.3.2
ok  	github.com/hashicorp/aws-sdk-go-base	0.864s
?   	github.com/hashicorp/aws-sdk-go-base/awsmocks	[no test files]
ok  	github.com/hashicorp/aws-sdk-go-base/awsv1shim	9.499s
ok  	github.com/hashicorp/aws-sdk-go-base/tfawserr	2.287s

I have no go.mod conflicts either.