Improve http connection reuse

[bmteller]

What this PR does:
Fixes connection reuse for S3 range requests and increases the number of MaxIdleConnsPerHost for the S3 backend to 100 to match the azure settings. Also, assumes GCP has the same connection reuse problem for range requests and performs the same fix. Note: I have tested the fix for S3 range requests and verified it is a problem and the change fixes the problem but I have not verified that it is a problem for GCP or that it fixes the problem for GCP. The GCP HTTP google storage code does look like it effectively returns the body reader so it does look like GCP would have a similar issue.

Which issue(s) this PR fixes:
Fixes #3750

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[CLAassistant]

All committers have signed the CLA.

[joe-elliott]

Thanks for working on this.

• Do you think we should put something similar in Azure?
• Can you add a changelog entry detailing the fix

[bmteller]

I don't think azure has a similar problem unless it is in the azure library itself.

        if _, err := blobClient.DownloadBuffer(ctx, destBuffer, &blob.DownloadBufferOptions{
                Range: blob.HTTPRange{
                        Offset: offset,
                        Count:  size,
                },
                BlockSize:   blob.DefaultDownloadBlockSize,
                Concurrency: maxParallelism,
                RetryReaderOptionsPerBlock: blob.RetryReaderOptions{
                        MaxRetries: maxRetries,
                },

and this blobClient is from github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob.

[bmteller]

what should it be classified in the changelog as? BUGFIX?

[joe-elliott]

what should it be classified in the changelog as? BUGFIX?

Yeah, I think that's fair.

[joe-elliott]

I went ahead and made the changelog entry b/c of how valuable this fix is.

Thanks!

[bmteller]

thanks Joe!