Add Endpoint number to OTA cluster

[holbrookt]

Problem

There is no way to blindly query for a singleton cluster on another node, which means that in order to send commands to an OTA Provider node, the sender will need to know the Endpoint number to contact.

Proposed Solution

The Endpoint number can be communicated via a field in the AnnounceOTAProvider command and the DefaultOTAProviders attribute list.

Context: https://github.com/CHIP-Specifications/connectedhomeip-spec/pull/4693