refactor: Add MtailDeployer

- This splits the existing deploy_mtail() routine into methods for the
  install, configure, and activate stages.

cmdeploy/src/cmdeploy/__init__.py

@@ -747,7 +747,13 @@ def deploy_turn_server(config):
     )
 
 
-def deploy_mtail(config):
+class MtailDeployer(Deployer):
+    def __init__(self, *, mtail_address, **kwargs):
+        super().__init__(**kwargs)
+        self.mtail_address = mtail_address
+
+    @staticmethod
+    def install_impl():
         # Uninstall mtail package, we are going to install a static binary.
         apt.packages(name="Uninstall mtail", packages=["mtail"], present=False)
 
@@ -770,15 +776,18 @@ def deploy_mtail(config):
             ],
         )
 
+    def configure_impl(self):
         # Using our own systemd unit instead of `/usr/lib/systemd/system/mtail.service`.
         # This allows to read from journalctl instead of log files.
         files.template(
-        src=importlib.resources.files(__package__).joinpath("mtail/mtail.service.j2"),
+            src=importlib.resources.files(__package__).joinpath(
+                "mtail/mtail.service.j2"
+            ),
             dest="/etc/systemd/system/mtail.service",
             user="root",
             group="root",
             mode="644",
-        address=config.mtail_address or "127.0.0.1",
+            address=self.mtail_address or "127.0.0.1",
             port=3903,
         )
 
@@ -792,14 +801,17 @@ def deploy_mtail(config):
             group="root",
             mode="644",
         )
+        self.need_restart = mtail_conf.changed
 
+    def activate_impl(self):
         systemd.service(
             name="Start and enable mtail",
             service="mtail.service",
-        running=bool(config.mtail_address),
+            running=bool(self.mtail_address),
-        enabled=bool(config.mtail_address),
+            enabled=bool(self.mtail_address),
-        restarted=mtail_conf.changed,
+            restarted=self.need_restart,
         )
+        self.need_restart = False
 
 
 class IrohDeployer(Deployer):
@@ -931,6 +943,7 @@ def deploy_chatmail(config_path: Path, disable_mail: bool) -> None:
 
     nginx_deployer = NginxDeployer(config=config)
     journald_deployer = JournaldDeployer()
+    mtail_deployer = MtailDeployer(mtail_address=config.mtail_address)
 
     all_deployers = [
         unbound_deployer,
@@ -941,6 +954,7 @@ def deploy_chatmail(config_path: Path, disable_mail: bool) -> None:
         postfix_deployer,
         nginx_deployer,
         journald_deployer,
+        mtail_deployer,
     ]
 
     #
@@ -1116,4 +1130,6 @@ def deploy_chatmail(config_path: Path, disable_mail: bool) -> None:
         mode="700",
     )
 
-    deploy_mtail(config)
+    mtail_deployer.install()
+    mtail_deployer.configure()
+    mtail_deployer.activate()