tv-casting-app: Add APIs to list all TV endpoints and sending commands to a specific endpoint

[sharadb-amazon]

Reproduction steps / Feature

Currently the tv-casting libs and apps send all media commands to endpointId 1. We should do the following instead:
1. Add API to list the endpoints available on a TV (using the descriptor cluster).
2. Update existing media command and subscription APIs to specify a specific endpointId to send the requests to.

This should be implemented and extended to Linux, android and iOS versions of the casting library.

Platform

android, darwin, raspi

Platform Version(s)

No response

Type

Manually tested with SDK

(Optional) If manually tested please explain why this is only manually tested

Tested using the tv-casting-apps for Linux, android and iOS and checked that all commands are being sent to endpointId 1.

Anything else?

No response