feat: add relay systemd install with enroll method

[sheensantoscapadngan]

Description 📣

This PR adds enrollment-based systemd installation for relays. The main changes are:

• Token enrollment before installing an org relay service.
• AWS authentication configuration for service startup.
• Positional relay names with legacy install compatibility.
• New relay environment keys and systemd configuration writers.

Type ✨

• Bug fix
• New feature
• Improvement
• Breaking change
• Documentation

Tests 🛠️

# Here's some code block to paste some code snippets

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• I have read the contributing guide, agreed and acknowledged the code of conduct. 📝

[infisical-review-police]

💬 Discussion in Slack: #pr-review-cli-323-feat-add-relay-systemd-install-with-enroll-method

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[veria-ai]

PR overview

All previously flagged issues have been addressed. No open security concerns remain on this pull request.

Security review

No open security issues remain on this pull request.

Fixed/addressed: 2 · PR risk: 0/10

[greptile-apps]

Greptile Summary

This PR adds enrollment-based systemd installation for relays. The main changes are:

• Token enrollment before installing an org relay service.
• AWS authentication configuration for service startup.
• Positional relay names with legacy install compatibility.
• New relay environment keys and systemd configuration writers.

Confidence Score: 4/5

Token-enrolled services can select the wrong startup path, and invalid enrollment methods can install the wrong authentication mode.

• The token systemd configuration omits the mode consumed by relay start.
• Unsupported method values fall through to the legacy org flow instead of being rejected.
• The AWS writer persists its startup mode correctly.

packages/relay/systemd.go and packages/cmd/relay.go

Important Files Changed

Filename	Overview
packages/cmd/relay.go	Adds token, AWS, instance, and legacy systemd installation branches; unsupported enrollment methods incorrectly enter the legacy branch.
packages/relay/enroll.go	Adds the environment key used to pass the selected enrollment method into relay startup.
packages/relay/systemd.go	Adds token and AWS systemd configuration writers, but the token writer omits its required startup mode.

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