Feature: support custom text colors in yjs collaboration awareness

## Description
In addition to supporting custom background colors for cursors and behind usernames when collaborating with Yjs, there should be support for overriding the color of the text used for the username, instead of it being hard coded to white.

Start by locating the Yjs collaboration awareness implementation and the existing handling for custom cursor and username background colors. Trace where the username text color is fixed to white, then verify that an override is supported while existing default coloring remains unchanged.

Written by the indexing model from the issue text.