Migrate away from @nodejs-github-bot tokens.

[avivkeller]

I think we should stop creating PATs associated with @nodejs-github-bot, and instead rely on the more secure alternative: GitHub App Tokens.

I've created a basic GitHub app that can be transferred into the org to replace @nodejs-github-bot.

WDYT?

[aduh95]

You probably need to include some details on why that would be a more secure alternative