Add pyinfra equivalent of 0x0I.systemd

[wowi42]

The 0x0I.systemd Ansible role is the #8 most-downloaded role on Ansible Galaxy (~11M downloads). This issue tracks adding a pyinfra equivalent as an example in this repo.

• Ansible Galaxy: https://galaxy.ansible.com/ui/standalone/roles/0x0I/systemd/
• Source: https://github.com/0x0I/ansible-role-systemd

Scope

• Port the role's core tasks to a pyinfra deploy / operations
• Manage systemd units (services, timers, mounts, etc.)
• Expose equivalent configurable variables
• Document usage in a README

cc @wowi42