TW-5092: add AUR package publishing to release pipeline

[qasim-nylas]

Summary

• Add GoReleaser aurs section to publish the Nylas CLI as an AUR package (nylas) on each release
• Add CI step to set up AUR SSH key with host key fingerprint verification before GoReleaser runs
• Add Arch Linux install instructions (yay -S nylas / paru -S nylas) to release notes template

Setup required

• Generate ed25519 SSH keypair and register public key with AUR account
• Add AUR_SSH_PRIVATE_KEY as a GitHub Actions secret
• Create the nylas package on AUR (initial push to reserve the name)

Test plan

• Verify goreleaser check passes with updated .goreleaser.yml
• Run a snapshot build (goreleaser release --snapshot --skip=publish) to confirm AUR section is valid
• Verify SSH key setup step runs correctly in CI (dry run on non-push event)
• After merging, confirm AUR package is published on next release tag

Related docs

• https://cli.nylas.com/docs/commands/init
• https://developer.nylas.com/docs/dev-guide/quickstart/

[AaronDDM]

LGTM 👍