replace track のサンプルを追加する

[voluntas]

This pull request introduces a new example for replacing media tracks in a WebRTC connection, along with some minor updates to the project configuration. The most important changes include adding a new example page, implementing the logic for the replace track functionality, and updating the project dependencies.

New Example for Replacing Tracks:

• examples/index.html: Added a link to the new replace track example.
• examples/replace_track/index.html: Created a new HTML page for the replace track example with input fields and buttons for connecting, replacing streams, disconnecting, and getting stats.
• examples/replace_track/main.mts: Implemented the logic for connecting to a WebRTC server, replacing media tracks, and handling various WebRTC events.

Project Configuration Updates:

• package.json: Updated the pnpm package manager version from 9.11.0 to 9.12.3.
• vite.config.mjs: Added the new replace track example to the Vite configuration for building.