ansible: update gh-bot server

[richardlau]

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Create a new Debian 12 server to replace the Debian 8 gh-bot server. Update the ansible/playbooks/create-github-bot.yml playbook to automate setup, including:

• Fetching of deployment secrets from the secrets repository.
• Generating the allowlist of jenkins-workspace IP addresses from the inventory.
• Restarting the services if required.

Fixes: https://github.com/nodejs/build/issues/3214

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This is deployed to the new server and I've updated the DNS entry for the bot in CloudFlare to the new IP address. We can remove the old server once we're happy the new one is operating without issues (or if we do find issues we can swap the DNS entry back to the old IP address).