[users] Add "transient" for hostname-location

src/modules/users/Config.cpp

@@ -84,7 +84,9 @@ hostNameActionNames()
     static const NamedEnumTable< HostNameAction > names {
         { QStringLiteral( "none" ), HostNameAction::None },
         { QStringLiteral( "etcfile" ), HostNameAction::EtcHostname },
-        { QStringLiteral( "hostnamed" ), HostNameAction::SystemdHostname }
+        { QStringLiteral( "etc" ), HostNameAction::EtcHostname },
+        { QStringLiteral( "hostnamed" ), HostNameAction::SystemdHostname },
+        { QStringLiteral( "transient" ), HostNameAction::Transient },
     };
     // clang-format on
     // *INDENT-ON*

src/modules/users/Config.h

@@ -25,6 +25,7 @@ enum class HostNameAction
     None,
     EtcHostname,  // Write to /etc/hostname directly
     SystemdHostname,  // Set via hostnamed(1)
+    Transient,  // Force target system transient, remove /etc/hostname
 };
 
 const NamedEnumTable< HostNameAction >& hostNameActionNames();

src/modules/users/SetHostNameJob.cpp

@@ -146,6 +146,9 @@ SetHostNameJob::exec()
         // Does its own logging
         setSystemdHostname( m_config->hostName() );
         break;
+    case HostNameAction::Transient:
+        CalamaresUtils::System::instance()->removeTargetFile( QStringLiteral( "/etc/hostname" ) );
+        break;
     }
 
     if ( m_config->writeEtcHosts() )

src/modules/users/users.conf

@@ -161,7 +161,9 @@ userShell: /bin/bash
 # - *location* How the hostname is set in the target system:
 #   - *None*, to not set the hostname at all
 #   - *EtcFile*, to write to `/etc/hostname` directly
+#   - *Etc*, identical to above
 #   - *Hostnamed*, to use systemd hostnamed(1) over DBus
+#   - *Transient*, to remove `/etc/hostname` from the target
 #   The default is *EtcFile*. Setting this to *None* will
 #   hide the hostname field.
 # - *writeHostsFile* Should /etc/hosts be written with a hostname for