feat: http-only-cookie-auth + refactor EC component

[Spiral-Memory]

Brief Title

HTTP-Only Cookie-Based Login, Refactoring EC Component

Acceptance Criteria Fulfillment

• [x] Reordered code for better readability.
• [x] Removed unnecessary global states that can be handled with existing ECOptions.
• [x] Cleaned up EmbeddedChat component and managed layout-related functions in ChatLayout.js.
• [x] Added AuthTokenEndpoint in RC-app to handle saving, retrieving, and deleting tokens as HTTP-only cookies.
• [x] Modified auth.js library functions to support both secure and localStorage-based login.
• [x] Added API calls in RocketChatAuth library.

Fixes #587

Video/Screenshots

https://github.com/RocketChat/EmbeddedChat/assets/78961432/24fdf4bf-34b5-4e66-b045-802d6fc428dd

[Spiral-Memory]

Hey @sidmohanty11

This PR is now ready for review. It mainly includes HTTP-only cookie-based authentication with the help of the EmbeddedChat RC app. It can handle all three scenarios: saving the token, getting the token, and deleting the token. When saveToken is called, the RC app will set an HTTP-only cookie. In all other requests, this token will always be included in the request. While getToken is called, the RC app will extract the token from the cookie and return it to the client. When deleting the token, the RC app will set an empty cookie in the browser. All of the functionality works fine and is shown in the video.

Other changes include cleaning up the EmbeddedChat component a little by removing all unnecessary global states (which can already be handled by ECOptions that's passed as context to all components, so using global states here is redundant). Additionally, all the layout-related functions have been moved to ChatLayout, and some minor issues have been fixed.

Kindly review this PR.

[sidmohanty11]

Awesome work!