Add goofys as user agent for s3 request

[monthonk]

This PR add "goofys/version-hash" to the user agent list for each request. You will be able to identify which requests come from goofys and which version if you enable server access logging or CloudTrail on your buckets.

example for debug_s3 log

2022/05/18 10:08:32.838728 s3.DEBUG DEBUG: Request s3/ListObjectsV2 Details:
---[ REQUEST POST-SIGN ]-----------------------------
GET /<REDACTED>?delimiter=%2F&list-type=2&prefix= HTTP/1.1
Host: s3.eu-west-1.amazonaws.com
User-Agent: goofys/0.24.0-829d8e5ce20faa3f9f6f054077a14325e00e9249 aws-sdk-go/1.38.7 (go1.18.2; linux; amd64)
Accept-Encoding: identity
Authorization: AWS4-HMAC-SHA256 Credential=<REDACTED>, SignedHeaders=host;x-amz-content-sha256;x-amz-date, Signature=<REDACTED>
X-Amz-Content-Sha256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
X-Amz-Date: 20220518T100832Z

example for server access log

fda01774e8671afabd99d08ccfcb4ef3a0fde3b84c04977a33cd49c863ac0b3e bucket-name [18/May/2022:10:07:30 +0000] <REDACTED> arn:aws:iam::<REDACTED>:user/<REDACTED> CVTB43X4F1MAXG2X REST.GET.OBJECT largefile "GET /bucket-name/largefile HTTP/1.1" 206 - 20971520 10240000000 685 128 "-" "goofys/0.24.0-829d8e5ce20faa3f9f6f054077a14325e00e9249 aws-sdk-go/1.38.7 (go1.18.2; linux; amd64)" - <REDACTED> SigV4 ECDHE-RSA-AES128-GCM-SHA256 AuthHeader s3.eu-west-1.amazonaws.com TLSv1.2 -

[dannycjones]

Looks good to me, I have run some basic tests locally (mount, list, read, unmount) on macOS against an eu-west-1 Amazon S3 Bucket.

[monthonk]

@kahing would you be able to take a look?

I also think it might be a good opportunity to release a new version after this is merged, it's been a while since the last version and things are starting to break.
I'm happy to help if there are any tests required before the release.