feat: Matrix Integration for EmbeddedChat

[Aryan-Verma-999]

feat: Matrix Integration for EmbeddedChat

Acceptance Criteria fulfillment

• [x] Integrate EmbeddedChat with the new Rocket.Chat native Matrix homeserver while keeping direct access to Rocket.Chat as an alternate option.
• [x] EmbeddedChat has a configuration option (mode prop) to choose between using the native Matrix homeserver and direct Rocket.Chat access.
• [x] When configured to use the native Matrix homeserver, EmbeddedChat can connect to a single configured channel, join it, and send and receive messages successfully.
• [x] Documentation is added explaining how to configure EmbeddedChat for the native Matrix homeserver and how to switch between Matrix and direct Rocket.Chat modes. Fixes #1029

Video/Screenshots

PR Test Details

1. Run yarn storybook.
2. Go to the EmbeddedChat story.
3. In the Controls panel, switch mode to matrix.
4. Enter a valid Matrix host (e.g., https://matrix.org) and roomId.
5. Log in and verify message sending/receiving.

Note: The PR will be ready for live testing at https://rocketchat.github.io/EmbeddedChat/pulls/pr-1030 after approval. Contributors are requested to replace <pr_number> with the actual PR number.