feat(Live Stream API): add channel clip samples and tests

[irataxy]

Description

Fixes b:341726237

Important: FFmpeg (https://www.ffmpeg.org/) must be installed in the test environment.

sudo apt install ffmpeg

Checklist

• [X] I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• [X] Tests pass: nox -s py-3.9 (see Test Environment Setup)
• [X] Lint pass: nox -s lint (see Test Environment Setup)
• [X] Please merge this PR for me once it is approved

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 4 region tags.

• video/live-stream/create_channel_clip.py:26, tag livestream_create_channel_clip
• video/live-stream/delete_channel_clip.py:23, tag livestream_delete_channel_clip
• video/live-stream/get_channel_clip.py:23, tag livestream_get_channel_clip
• video/live-stream/list_channel_clips.py:23, tag livestream_list_channel_clips

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