S3 config file default to empty string

[aspacca]

Enhancement

What does this PR do?

Set default S3_CONFIG_FILE env variable

Why is it important?

This helps users not to have to remember the environment variable name, see the format of the value and more easily set the S3 URI value to the config file.

Checklist

• My code follows the style guidelines of this project
  - [ ] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
  - [ ] I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.md

Author's Checklist

• [ ]

How to test this PR locally

Related issues

Closes #85

Use cases

Screenshots

Logs

[elasticmachine]

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• Start Time: 2022-03-02T02:59:04.646+0000

• Duration: 17 min 26 sec

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Test	Results
Failed	0
Passed	56
Skipped	0
Total	56

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