esp_capture: fix bitrate setter for video/audio; plumb to encoder (AUD-6880)

[josefeliuf]

This PR fixes #29: runtime bitrate control for esp_capture by correctly forwarding sink bitrate changes to the capture path manager and ultimately the video encoder element.

1. What was wrong

The current esp_capture_sink_set_bitrate(...) returned ESP_CAPTURE_ERR_NOT_SUPPORTED and mixed audio/video handling, so bitrate updates never reached the GMF video encoder.

2. What this changes

Dispatches by stream_type and calls path_mngr->set(..., ESP_CAPTURE_PATH_SET_TYPE_{VIDEO|AUDIO}_BITRATE, ...), which stores the bitrate and applies it immediately if the encoder element is already created (or on prepare/start otherwise).

3. Motivation / context

I’m using espressif/esp-webrtc-solution for a WebRTC sender pipeline. That repo uses esp_capture for media but currently does not expose a public API to change bitrate at runtime, so I added a small wrapper on that side which calls into esp_capture_sink_set_bitrate(...). I plan to open a companion PR in esp-webrtc-solution to expose this API officially. The esp-webrtc-solution README explicitly lists esp_capture as the media capture component.
GitHub

4. Testing

Environment

ESP-IDF: latest

Board: ESP32-P4

Verified return code is OK and visual quality/throughput adapts; logs show the encoder path receiving updated bitrate.

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.