Extend text mimeTypes to support VTT

[DenisPalnitsky]

Pull Request Template

Summary

This PR adds support of VTT (Zoom audio transcript) file mime type.

Corresponding issue: #4562

Change Type

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• 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 not work as expected)
• This change requires a documentation update
• Translation update

Testing

Upload VTT file. This should work

Checklist

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• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes
• Any changes dependent on mine have been merged and published in downstream modules.