Allow adding files to .gitignore (#38089)

This feature allows users to add a new, untracked file to `.gitignore`
by using the context menu in the git panel.

<img width="300" alt="Demo screen shot"
src="https://github.com/user-attachments/assets/3f2402fb-9337-42f8-939f-dac12ca09518"
/>

Release Notes:

- Added feature to add a new file to `.gitignore`
681c19899frobert7k committed on 10/8/2025, 9:49:06 PM· committed by GitHubparent439add3
2 files changedLine totals unavailable