doc: add emissary introduction

doc/fr/resources/overview.plantuml

@@ -0,0 +1,55 @@
+@startuml
+top to bottom direction
+skinparam linetype ortho
+
+node PilotNode as "Pilot Node" {
+    database DataStore as "Data Store"
+
+    component EmissaryServer as "Emissary Server" {
+
+        component SpecificationRegistry as "Specification Registry" {
+            component UCISpecification as "UCI Spec"
+
+            component MDNSSpecification as "mDNS Spec"
+
+            component AppSpecification as "App Spec"
+
+            component ProxySpecification as "Proxy Spec"
+        }
+
+        component HTTPAPIHandler as "HTTP API Handler"
+
+        HTTPAPIHandler .down.> SpecificationRegistry: validates agents data with
+
+        HTTPAPIHandler .right.> DataStore: saves agent data in
+    }
+}
+
+node OpenWRTNode as "OpenWRT Node" {
+    component EmissaryAgent as "Emissary Agent" {
+
+        component StateManager as "State Manager"
+
+        StateManager --up-> HTTPAPIHandler: fetches specs from
+
+        component UCIController as "UCI Controller"
+
+        UCIController -up-> StateManager: reconciles with
+
+        component SysupgradeController as "Sysupgrade Controller"
+
+        SysupgradeController -up-> StateManager: reconciles with
+
+        component ProxyController as "Proxy Controller"
+
+        ProxyController -up-> StateManager: reconciles with
+
+        component MDNSController as "mDNS Controller"
+
+        MDNSController -up-> StateManager: reconciles with
+
+        component AppController as "App Controller"
+
+        AppController -up-> StateManager: reconciles with
+    }
+}