Feature/add transcoded url meta

[pranvinit]

Types of changes

What types of changes does your code introduced to project?
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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. Add a _rt_transcoded_url meta field to the attachment to save the transcoded URL.
2. Add an editable URL form field in the media modal.
3. Add a toggle to set Adaptive Bitrate Streaming in the transcoder settings page.
4. WIP: Progress bar functionality.

Checklist

Put an x in the boxes that apply.

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

Closing issues

• Issue Link