Open new tab with random color.

# Description of the new feature/enhancement

Currently we have to manualy assign color to a tab when we open one. If there is feature which can assign random color to a new tab then it will be a good. First it looks cool and second it easy easiar to navigate to tabs.

The issue names no files, tests, or entry points. Start by locating new-tab creation and the existing tab-color behavior in the Windows Terminal codebase, then determine how colors are assigned. Done means a newly opened tab receives a random color without manual assignment.

Written by the indexing model from the issue text.