(feat): make S3 transfer concurrency, part size, checksum configurable

[gowrisankar22]

same changes as cloudfoundry/bosh-s3cli#61

1. Problem

2. The BOSH S3 CLI currently uses AWS SDK V2 defaults for S3 uploads and downloads, which are significantly lower than other CLI tools, resulting in suboptimal performance example for https://docs.cloud.google.com/distributed-cloud/docs

• Default Upload/Download Concurrency: 5
• Default Upload/Download Part Size: 5MB

https://pkg.go.dev/github.com/aws/aws-sdk-go-v2/feature/s3/manager#Downloader

These conservative defaults were designed for general-purpose use cases but create a bottleneck for BOSH operations that require higher throughput. Unlike the AWS CLI, which offers tunable parameters, there was no way for users to optimize transfer performance based on their specific infrastructure requirements and network conditions.

Solution
This PR makes S3 transfer concurrency and part size configurable, allowing operators to:

• Increase parallel transfer threads to match available network bandwidth and client machine capabilities
• Optimize multipart upload/download sizes for specific network conditions and storage backend characteristics
• Enable throughput optimization without being constrained by conservative SDK defaults.

These properties are purely optional and users can choose if they really need to change the default behavior. At least for google's new air-gapped offering we needed. https://docs.cloud.google.com/distributed-cloud/docs

2. Problem
   AWS SDK Compatibility (CRC64NVME): The latest bosh-s3cli uses the newest AWS SDK V2, which defaults to x-amz-sdk-checksum-algorithm:CRC64NVME. This has caused compatibility issues to GDCH.

Solution
In the interim, we have to disable this behavior using the configurable parameter disable_checksums.

Minor improvement --> fixing the pascalcase for RequestChecksumCalculationEnabled and UploaderRequestChecksumCalculationEnabled

[serdarozerr]

looks good, just some minor suggestions

[a-hassanin]

LGTM