FCE-2749 Add protos for image capture for agents

[Qizot]

Description

Describe your changes.

Motivation and Context

Why is this change required? What problem does it solve? If it fixes an open
issue, please link to the issue here.

Documentation impact

• Documentation update required
• Documentation updated in another PR
• No documentation update required

[linear]

FCE-2749 Add new agent request to protos for image capture

[Copilot]

Pull request overview

This PR adds protocol buffer definitions to support image capture functionality for agents. The changes introduce new message types that allow agents to request image captures from tracks and receive the captured images as responses.

Changes:

• Added CaptureImage request message to allow agents to request image capture from a specific track
• Added TrackImage response message to return captured image data with content type information
• Updated documentation to reflect the new message types

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
fishjam/agent_notifications.proto	Defines the new CaptureImage and TrackImage protobuf messages for image capture requests and responses
fishjam_protos/lib/fishjam/agent_notifications.pb.ex	Generated Elixir code from the proto definitions, adding the corresponding modules and fields
doc/docs.md	Documentation updates for the new message types in the API reference

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