Onboarding sxa as a releaser

[BethGriggs]

@sxa has prepared two releases (nodejs/node#42254, nodejs/node#42285) 🎉

We now need to complete the remaining onboarding actions (from GOVERNANCE.md):

• Be added to the GitHub releasers team in the Node.js org (grants ci-release access)
• Be added to the GitHub security-release team in the Node.js and nodejs-private orgs
• Have a single, high quality SSH key added to the "dist" user on the primary www server
• Have a GPG key added to the nodejs/node README.md
  • The key should be cherry-picked to all active release branches.
• Open a PR in nodejs/docker-node to add gpg key to node.keys
• Add the key to https://github.com/nodejs/release-keys