fix: added option to set fps in video metadata according to the documentation

[philipshurpik]

FPS option is missed in class VideoMetadata(proto.Message) in types/content.py
both in v1 and v1beta1

It should exist according to both docs (v1 and v1beta1):
https://cloud.google.com/vertex-ai/generative-ai/docs/reference/rest/v1/Content
https://cloud.google.com/vertex-ai/generative-ai/docs/reference/rest/v1beta1/Content

And also is existent in VideoMetadata in content.proto:
https://github.com/googleapis/googleapis/blob/97763d6efb2d35474e0363c254ee6994837a08fa/google/ai/generativelanguage/v1/content.proto#L107

I implemented it's support according to proto file and documentation.
Tested locally that library version with this changes is actually working by using less 'input_tokens'.
Also added using of fps field in few tests to the existing video_metadata object

Fixes #6073 🦕

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