gcs: use MD5Sum as ETag if present in object attrs

[poornas]

Fixes: 7642

Description

for single PUT object call on GCS gateway - use the MD5 object attribute if set. Otherwise use the CRC32c hash as it is guaranteed to be present.

Motivation and Context

This would allow md5 compatibility in --compat mode

Regression

No

How Has This Been Tested?

see repro steps in issue

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added unit tests to cover my changes.
• I have added/updated functional tests in mint. (If yes, add mint PR # here: )
• All new and existing tests passed.

[minio-ops]

Mint Automation

Test	Result
mint-compression-xl.sh	✔️
mint-compression-dist-xl.sh	✔️
mint-compression-fs.sh	✔️
mint-worm.sh	✔️
mint-fs.sh	✔️
mint-dist-xl.sh	✔️
mint-gateway-nas.sh	✔️
mint-xl.sh	❌ more...
mint-large-bucket.sh	❌ more...

7643-74732f3/mint-xl.sh.log:

Running with
SERVER_ENDPOINT:      72.28.97.61:30068
ACCESS_KEY:           minio
SECRET_KEY:           ***REDACTED***
ENABLE_HTTPS:         0
SERVER_REGION:        us-east-1
MINT_DATA_DIR:        /mint/data
MINT_MODE:            full
ENABLE_VIRTUAL_STYLE: 0

To get logs, run 'docker cp ebb582a47e05:/mint/log /tmp/mint-logs'

(1/14) Running aws-sdk-go tests ... FAILED in 6 minutes and 0 seconds
{
  "alert": "",
  "args": {
    "bucketName": "aws-sdk-go-test-gnssbs1mbskacs",
    "expiry": 60000000000,
    "objectName": "presignedTest"
  },
  "duration": 360010,
  "error": "XMinioServerNotInitialized: Server not initialized, please try again.\n\tstatus code: 503, request id: 159EA0BF8CB34385, host id: ",
  "function": "PresignedPut",
  "message": "AWS SDK Go CreateBucket Failed",
  "name": "aws-sdk-go",
  "status": "FAIL"
}

Executed 0 out of 14 tests successfully.

7643-74732f3/mint-large-bucket.sh.log:

Running with
SERVER_ENDPOINT:      72.28.97.61:31395
ACCESS_KEY:           minio
SECRET_KEY:           ***REDACTED***
ENABLE_HTTPS:         0
SERVER_REGION:        us-east-1
MINT_DATA_DIR:        /mint/data
MINT_MODE:            full
ENABLE_VIRTUAL_STYLE: 0

To get logs, run 'docker cp a2d0eca434ac:/mint/log /tmp/mint-logs'

(1/14) Running aws-sdk-go tests ... done in 2 seconds
(2/14) Running aws-sdk-java tests ... done in 1 seconds
(3/14) Running aws-sdk-php tests ... done in 50 seconds
(4/14) Running aws-sdk-ruby tests ... FAILED in 4 minutes and 10 seconds
{
  "name": "aws-sdk-ruby",
  "function": "copyObject(source_bucket_name, target_bucket_name, source_file_name, target_file_name = )",
  "args": {
    "source_bucket_name": "aws-sdk-ruby-bucket-363c79a3fe35",
    "target_bucket_name": "aws-sdk-ruby-bucket-f66d9b8bd146",
    "source_file_name": "datafile-1-kB",
    "target_file_name": "datafile-1-kB"
  },
  "duration": 242482.76,
  "error": "Net::ReadTimeout",
  "status": "FAIL"
}

Executed 3 out of 14 tests successfully.

[codecov]

Codecov Report

Merging #7643 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #7643      +/-   ##
==========================================
+ Coverage   47.27%   47.28%   +0.01%     
==========================================
  Files         294      294              
  Lines       47172    47176       +4     
==========================================
+ Hits        22300    22308       +8     
+ Misses      22799    22796       -3     
+ Partials     2073     2072       -1

Impacted Files	Coverage Δ
cmd/gateway/gcs/gateway-gcs.go	22.19% <100%> (+0.29%)	⬆️
cmd/fs-v1.go	61.57% <0%> (-0.38%)	⬇️
cmd/posix.go	62.4% <0%> (+0.38%)	⬆️
cmd/bitrot-streaming.go	86.95% <0%> (+3.26%)	⬆️

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