systemd(user): add podman unit, slice files

* podman user service (rootless) is autostarted (enabled)

.config/systemd/user/podman.service

@@ -0,0 +1,19 @@
+[Unit]
+Description=Podman API Service
+Requires=podman.socket
+After=podman.socket
+Documentation=man:podman-system-service(1)
+StartLimitIntervalSec=0
+
+[Service]
+Slice=podman.slice
+; Delegate=yes
+Delegate=cpu cpuset memory pids io
+Type=exec
+KillMode=process
+Environment=LOGGING="--log-level=info"
+ExecStart=/usr/bin/podman --cgroup-manager=systemd $LOGGING system service
+
+[Install]
+; WantedBy=multi-user.target
+WantedBy=sway-session.target

.config/systemd/user/podman.slice

@@ -0,0 +1,18 @@
+[Unit]
+Description=Slice that limits podman resources
+Before=slices.target
+# refs:
+#  https://baykara.medium.com/docker-resource-management-via-cgroups-and-systemd-633b093a835c
+#  https://docs.docker.com/engine/reference/commandline/dockerd/#docker-runtime-execution-op>
+
+[Slice]
+CPUAccounting=yes
+# 100% is an equivalent of full utilization on a single core
+# we allow for 85% here - applies to all docker.service-spawn
+# processes cumulatively
+# CPUQuota=85%
+CPUQuota=50%
+MemoryAccounting=yes
+MemoryHigh=10G
+MemoryMax=12G
+MemorySwapMax=1G

.config/systemd/user/sway-session.target.wants/podman.service

@@ -0,0 +1 @@
+../podman.service