AWS SDK for Go v2 MaxBackoff delay to match AWS SDK for Go v1 default

[ewbankkit]

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Closes #1009.

Changes the AWS SDK for Go v2 MaxBackoff delay to 300 seconds, the AWS SDK for Go v1 default.

% go test ./...
?   	github.com/hashicorp/aws-sdk-go-base/v2/configtesting	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/internal/awsconfig	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/internal/constants	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/internal/errs	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/internal/slices	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/internal/test	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/mockdata	[no test files]
?   	github.com/hashicorp/aws-sdk-go-base/v2/servicemocks	[no test files]
ok  	github.com/hashicorp/aws-sdk-go-base/v2	5.940s
ok  	github.com/hashicorp/aws-sdk-go-base/v2/diag	(cached)
ok  	github.com/hashicorp/aws-sdk-go-base/v2/internal/config	0.717s
ok  	github.com/hashicorp/aws-sdk-go-base/v2/internal/endpoints	(cached)
ok  	github.com/hashicorp/aws-sdk-go-base/v2/internal/expand	(cached)
ok  	github.com/hashicorp/aws-sdk-go-base/v2/logging	0.595s
ok  	github.com/hashicorp/aws-sdk-go-base/v2/tfawserr	(cached)
ok  	github.com/hashicorp/aws-sdk-go-base/v2/useragent	0.777s
ok  	github.com/hashicorp/aws-sdk-go-base/v2/validation	(cached)

[jar-b]

LGTM 👍