fix(ENGDESK-26922): Make login_token optional

[farhat-ha]

Creating a client no longer requires login_tokento be passed. This is to allow users to login with username and password without TypeScripts errors.

Describe your changes

📝 To Do

• All linters pass
• All tests pass
• Change documentation based on my changes

✋ Manual testing

1. Provide manual testing instructions

🦊 Browser testing

1. navigate to packages/js
2. run yarn build
3. run yarn link
4. go to a webrtc project and run the yarn link @telnyx/webrtc
5. This code should not throw typecheck errors.

const client = new TelnyxRTC({
login: "login",
password: "password"
})

Desktop

• Edge (latest)
• Chrome
• Firefox
• Safari

📸 Screenshots

Description	Screenshot
Desktop
usage.gif