Add publisher initial video bitrate API

[CrckerSun]

Summary

• add Room.setPublisherInitialVideoBitrate for configuring the publisher PeerConnection
• set the WebRTC current and maximum video bitrate through PeerConnection.setBitrate
• add regression coverage and release metadata

Motivation

VideoEncoding.maxBitrate only caps the sender encoding bitrate and does not initialize libwebrtc's current target bitrate. This API allows clients to seed the publisher bitrate after connecting, which is particularly useful for H.264 publishing.

Validation

• ./gradlew :livekit-android-test:testDebugUnitTest --tests io.livekit.android.room.RTCEngineMockE2ETest.setPublisherInitialVideoBitrate
• ./gradlew spotlessCheck

[changeset-bot]

🦋 Changeset detected

Latest commit: 6efded5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
client-sdk-android	Minor

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