Cherry-pick #24426 to 7.x: Add tests for encoding setting of filestream input

[kvch]

Cherry-pick of PR #24426 to 7.x branch. Original message:

What does this PR do?

Add support for configuring encoding and adds migrates related tests from test_harvester.py.

Why is it important?

Previously encoding could not be configured correctly from configure. The underlying feature works it is already covered by numerous unit tests.

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.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Build stats

• Build Cause: Pull request #24629 opened

• Start Time: 2021-03-18T12:51:48.671+0000

• Duration: 75 min 48 sec

• Commit: 795884c

Test stats 🧪

Test	Results
Failed	0
Passed	13125
Skipped	2257
Total	15382

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Test stats 🧪

Test	Results
Failed	0
Passed	13125
Skipped	2257
Total	15382