Fix: unsigned s5cmd requests and also add option to disable s5cmd

[bhimrazy]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

• Enables support for unsigned requests with s5cmd to pass as storage options

   storage_options = {
    "AWS_NO_SIGN_REQUEST": "Yes",
    "S3_ENDPOINT_URL": "endpoint-url",
    }
  

• Adds an option to disable s5cmd
• Add test cases
• Update README

Fixes #511.

PR review

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79%. Comparing base (32659a6) to head (2674f80).
Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #513   +/-   ##
===================================
  Coverage    79%    79%           
===================================
  Files        39     39           
  Lines      5848   5859   +11     
===================================
+ Hits       4605   4621   +16     
+ Misses     1243   1238    -5     

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[tchaton]

Beautiful