feature: add REST endpint for ffmpeg server callback handler

[pranvinit]

Types of changes

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• Bugfix (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)
• Documentation Update

Details

1. Create a new /transcoder-callback REST API endpoint to handle the response of the FFMPEG transcoding server.
2. Does not change the existing callback_handler function implementation.

Checklist

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• Lint and tests pass locally with my changes
• I have added necessary documentation (if appropriate)

Closing issues

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Code analysis identified issues

action-phpcs-code-review has identified potential problems in this pull request during automated scanning. We recommend reviewing the issues noted and that they are resolved.

phpcs scanning turned up:

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Code analysis identified issues

action-phpcs-code-review has identified potential problems in this pull request during automated scanning. We recommend reviewing the issues noted and that they are resolved.

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