Add video API snippets

[ydumburs]

This pull request adds new Python snippets for Unified Video.

Changes:

• Created a 'video' folder and added video code snippets.
• Added video-related environment variables to .env.dist.

Includes:

• All the requests based on our developer guide: https://developer.vonage.com/en/video/server-sdks/python

Let me know if any adjustments or changes are needed. Happy to make updates.

[ydumburs]

Additional note: While working on the add_stream_to_archive functionality, I noticed that the usage example at https://developer.vonage.com/en/video/server-sdks/python didn't work as-is. Specifically, it seems that AddStreamRequest must be passed as a named argument ("params=...") instead of a positional one. Otherwise, it raises a syntax error. The method is defined like this: https://github.com/Vonage/vonage-python-sdk/blob/a8dbf81c818093e91c2ce8619c99ad5de9b6976a/video/src/vonage_video/video.py#L439 Because of this. the snippet I included differ slightly from the developer guide. The same adjustment is also applied to add_stream_to_broadcast, which uses the same AddStreamRequest model and method structure.