feat(systemd): Manage After dependencies

[jouir]

Allow nginx to be started after a list of systemd units (disabled by default).

Proposed changes

If nginx is listening to a tailscale IP address, the tailscaled.service unit must be started (and the IP address must be assigned) before starting nginx. Otherwise, the service will fail to start and the service will not survive a reboot. This commit allows to define nginx_service_after variable to eventually add a list of units separated by whitespaces.

Checklist

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• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added Molecule tests that prove my fix is effective or that my feature works.
• If applicable, I have checked that any relevant Molecule tests pass after adding my changes.
• I have updated any relevant documentation (defaults/main/*.yml, README.md and CHANGELOG.md).

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
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[jouir]

I have hereby read the F5 CLA and agree to its terms