Implement Liquid Leak Detector

Implement liquid leak detector based on design
https://gerrit.openbmc.org/c/openbmc/docs/+/73152.

Related PRs:
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/73151
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/73707
https://gerrit.openbmc.org/c/openbmc/sdbusplus/+/75461
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/75999

Tested:
```
>> busctl tree xyz.openbmc_project.LeakDetector
└─ /xyz
  └─ /xyz/openbmc_project
    └─ /xyz/openbmc_project/state
      └─ /xyz/openbmc_project/state/leak
        └─ /xyz/openbmc_project/state/leak/detector
          ├─ /xyz/openbmc_project/state/leak/detector/TrayDetector1
          └─ /xyz/openbmc_project/state/leak/detector/TrayDetector2

>> echo pull-up > /sys/devices/platform/gpio-sim.0/gpiochip2/sim_gpio0/pull

>> curl -k -H "X-Auth-Token: $token" -X GET https://${bmc}/redfish/v1/Systems/system/LogServices/EventLog/Entries
{
  "@odata.id": "/redfish/v1/Systems/system/LogServices/EventLog/Entries",
  "@odata.type": "#LogEntryCollection.LogEntryCollection",
  "Description": "Collection of System Event Log Entries",
  "Members": [
  	...
    {
      "@odata.id": "/redfish/v1/Systems/system/LogServices/EventLog/Entries/2",
      "@odata.type": "#LogEntry.v1_9_0.LogEntry",
      "AdditionalDataURI": "/redfish/v1/Systems/system/LogServices/EventLog/Entries/2/attachment",
      "Created": "2024-05-10T06:40:30.423+00:00",
      "EntryType": "Event",
      "Id": "2",
      "Message": "xyz.openbmc_project.State.Leak.Detector.LeakDetectedWarning",
      "Modified": "2024-05-10T06:40:30.423+00:00",
      "Name": "System Event Log Entry",
      "Resolved": false,
      "Severity": "Warning"
    }
  ],
  "Members@odata.count": 2,
  "Name": "System Event Log Entries"
}

>> echo pull-down > /sys/devices/platform/gpio-sim.0/gpiochip2/sim_gpio0/pull

>> curl -k -H "X-Auth-Token: $token" -X GET https://${bmc}/redfish/v1/Systems/system/LogServices/EventLog/Entries
{
  "@odata.id": "/redfish/v1/Systems/system/LogServices/EventLog/Entries",
  "@odata.type": "#LogEntryCollection.LogEntryCollection",
  "Description": "Collection of System Event Log Entries",
  "Members": [
	...
    {
      "@odata.id": "/redfish/v1/Systems/system/LogServices/EventLog/Entries/2",
      "@odata.type": "#LogEntry.v1_9_0.LogEntry",
      "AdditionalDataURI": "/redfish/v1/Systems/system/LogServices/EventLog/Entries/2/attachment",
      "Created": "2024-05-10T06:40:30.423+00:00",
      "EntryType": "Event",
      "Id": "2",
      "Message": "xyz.openbmc_project.State.Leak.Detector.LeakDetectedWarning",
      "Modified": "2024-05-10T06:42:23.989+00:00",
      "Name": "System Event Log Entry",
      "Resolved": true,
      "Severity": "Warning"
    },
    {
      "@odata.id": "/redfish/v1/Systems/system/LogServices/EventLog/Entries/3",
      "@odata.type": "#LogEntry.v1_9_0.LogEntry",
      "AdditionalDataURI": "/redfish/v1/Systems/system/LogServices/EventLog/Entries/3/attachment",
      "Created": "2024-05-10T06:42:24.024+00:00",
      "EntryType": "Event",
      "Id": "3",
      "Message": "xyz.openbmc_project.State.Leak.Detector.LeakDetectedNormal",
      "Modified": "2024-05-10T06:42:24.024+00:00",
      "Name": "System Event Log Entry",
      "Resolved": false,
      "Severity": "OK"
    }
  ],
  "Members@odata.count": 3,
  "Name": "System Event Log Entries"
}
```

Change-Id: Id6981deb314ca6852c5e31b932b28e601c2f3976
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/src/SystemdInterface.cpp b/src/SystemdInterface.cpp
new file mode 100644
index 0000000..fd41506
--- /dev/null
+++ b/src/SystemdInterface.cpp
@@ -0,0 +1,52 @@
+#include "SystemdInterface.hpp"
+
+#include <phosphor-logging/lg2.hpp>
+#include <sdbusplus/async.hpp>
+#include <sdbusplus/message/native_types.hpp>
+
+#include <exception>
+#include <string>
+#include <variant>
+
+PHOSPHOR_LOG2_USING;
+
+namespace systemd
+{
+
+auto SystemdInterface::startUnit(sdbusplus::async::context& ctx,
+                                 std::string sysdUnit)
+    -> sdbusplus::async::task<>
+{
+    if (sysdUnit.empty())
+    {
+        error("sysdUnit is empty");
+        co_return;
+    }
+
+    try
+    {
+        constexpr auto systemd =
+            sdbusplus::async::proxy()
+                .service("org.freedesktop.systemd1")
+                .path("/org/freedesktop/systemd1")
+                .interface("org.freedesktop.systemd1.Manager");
+
+        std::variant<sdbusplus::message::object_path> jobObjectPath =
+            co_await systemd
+                .call<std::variant<sdbusplus::message::object_path>>(
+                    ctx, "StartUnit", sysdUnit, "replace");
+
+        debug("Started {UNIT} with {JOBID}", "UNIT", sysdUnit, "JOBID",
+              std::get<sdbusplus::message::object_path>(jobObjectPath));
+    }
+    catch (const std::exception& e)
+    {
+        warning("Failed to start {UNIT}: {ERROR}", "UNIT", sysdUnit, "ERROR",
+                e);
+        co_return;
+    }
+
+    co_return;
+}
+
+} // namespace systemd