docs(samples): add code samples

[irataxy]

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• Appropriate docs were updated (if necessary)

Fixes 202972981

[snippet-bot]

Here is the summary of changes.

You are about to add 20 region tags.

• samples/snippets/create_cdn_key.py:24, tag video_stitcher_create_cdn_key
• samples/snippets/create_live_session.py:25, tag video_stitcher_create_live_session
• samples/snippets/create_slate.py:24, tag video_stitcher_create_slate
• samples/snippets/create_vod_session.py:24, tag video_stitcher_create_vod_session
• samples/snippets/delete_cdn_key.py:23, tag video_stitcher_delete_cdn_key
• samples/snippets/delete_slate.py:23, tag video_stitcher_delete_slate
• samples/snippets/get_cdn_key.py:23, tag video_stitcher_get_cdn_key
• samples/snippets/get_live_ad_tag_detail.py:25, tag video_stitcher_get_live_ad_tag_detail
• samples/snippets/get_live_session.py:23, tag video_stitcher_get_live_session
• samples/snippets/get_slate.py:23, tag video_stitcher_get_slate
• samples/snippets/get_vod_ad_tag_detail.py:23, tag video_stitcher_get_vod_ad_tag_detail
• samples/snippets/get_vod_session.py:24, tag video_stitcher_get_vod_session
• samples/snippets/get_vod_stitch_detail.py:25, tag video_stitcher_get_vod_stitch_detail
• samples/snippets/list_cdn_keys.py:22, tag video_stitcher_list_cdn_keys
• samples/snippets/list_live_ad_tag_details.py:24, tag video_stitcher_list_live_ad_tag_details
• samples/snippets/list_slates.py:22, tag video_stitcher_list_slates
• samples/snippets/list_vod_ad_tag_details.py:24, tag video_stitcher_list_vod_ad_tag_details
• samples/snippets/list_vod_stitch_details.py:24, tag video_stitcher_list_vod_stitch_details
• samples/snippets/update_cdn_key.py:24, tag video_stitcher_update_cdn_key
• samples/snippets/update_slate.py:23, tag video_stitcher_update_slate

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[parthea]

Wait for cl/440154661