Remove credential config of GetBucketRegion by default

[wty-Bryant]

The s3 transfer manager helper func GetBucketRegion is ported from go v1 but missed default anonymous credential config, this PR patches the config back so user could get a public bucket's region without credentials.
Fixes #3077

[Juneezee]

Thanks for fixing the bug!

Out of curiosity, is there a reason why we don't just set options.Credentials = nil directly in clientOptionFns[0]?

Suggested change

	clientOptionFns[0] = func(options *s3.Options) {
	options.APIOptions = append(options.APIOptions, captureBucketRegion.RegisterMiddleware)
	}
	copy(clientOptionFns[1:], optFns)
	clientOptionFns[1] = func(options *s3.Options) {
	options.Credentials = nil
	}
	copy(clientOptionFns[2:], optFns)
	clientOptionFns[0] = func(options *s3.Options) {
	options.APIOptions = append(options.APIOptions, captureBucketRegion.RegisterMiddleware)
	options.Credentials = nil
	}
	copy(clientOptionFns[1:], optFns)

[wty-Bryant]

It's just a idioms when I want to add a new functional config

[cartermckinnon]

@lucix-aws this broke things for private buckets in cn-northwest-1. The HeadBucket behavior is different there, you must provide credentials or you receive a 401 (and there is no x-amz-bucket-region header in the response).

It works as expected in cn-north-1 (even for buckets that reside in cn-northwest-1). I reached out to the S3 team as well, not clear if this is expected behavior.

I can work around this by explicitly using the client's credentials for the call:

cfg, _ := config.LoadDefaultConfig(context.TODO())
region, err := manager.GetBucketRegion(context.TODO(), s3.NewFromConfig(cfg), bucketName, func(o *s3.Options) {
	o.Credentials = cfg.Credentials
})

But this worked with defaults prior to feature/s3/manager@v1.17.75.