Add Option to Not Prompt for Authentication on Startup

**Is your feature request related to a problem? Please describe.**


I don't want to sign in to my GitHub account, but every time I open VSCode with this plugin installed I'm prompted by this notification to sign in. There doesn't appear to be any way to say "Don't remind me again"

**Describe the solution you'd like**

Some way to say that I don't want to be prompted to sign in with my github account every time I open VSCode.

The issue names no files, tests, or entry points. Trace the extension's startup authentication flow and identify where the sign-in notification is triggered and where user preferences are stored. Done means users can opt out of repeated prompts while users who want authentication can still sign in.

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