Impersonate as Icinga user, not root

This requires write permissions for

- etc/features-*
- etc/*.conf
- var/{lib,cache}/icinga2/*

Typically permissions are handled by prepare-dirs,
or the respective CLI commands are run as root either way.

fixes #4947

lib/cli/apisetupcommand.cpp

@@ -24,7 +24,7 @@ String ApiSetupCommand::GetShortDescription() const
 
 ImpersonationLevel ApiSetupCommand::GetImpersonationLevel() const
 {
-	return ImpersonateRoot;
+	return ImpersonateIcinga;
 }
 
 int ApiSetupCommand::GetMaxArguments() const

lib/cli/featuredisablecommand.cpp

@@ -36,7 +36,7 @@ int FeatureDisableCommand::GetMaxArguments() const
 
 ImpersonationLevel FeatureDisableCommand::GetImpersonationLevel() const
 {
-	return ImpersonateRoot;
+	return ImpersonateIcinga;
 }
 
 /**

lib/cli/featureenablecommand.cpp

@@ -36,7 +36,7 @@ int FeatureEnableCommand::GetMaxArguments() const
 
 ImpersonationLevel FeatureEnableCommand::GetImpersonationLevel() const
 {
-	return ImpersonateRoot;
+	return ImpersonateIcinga;
 }
 
 /**

lib/cli/nodesetupcommand.cpp

@@ -71,7 +71,7 @@ std::vector<String> NodeSetupCommand::GetArgumentSuggestions(const String& argum
 
 ImpersonationLevel NodeSetupCommand::GetImpersonationLevel() const
 {
-	return ImpersonateRoot;
+	return ImpersonateIcinga;
 }
 
 /**

lib/cli/nodewizardcommand.cpp

@@ -37,7 +37,7 @@ String NodeWizardCommand::GetShortDescription() const
 
 ImpersonationLevel NodeWizardCommand::GetImpersonationLevel() const
 {
-	return ImpersonateRoot;
+	return ImpersonateIcinga;
 }
 
 int NodeWizardCommand::GetMaxArguments() const