Add the ROUTER_LATE role & supporting fields (#632)

Will always rebroadcast packets, but will do so after all other modes.
Intended for router nodes that are there to provide additional coverage
in areas not already covered by other routers, or to bridge around
problematic terrain, but should not be given priority over other routers
in order to avoid unnecessarily consuming hops.

meshtastic/config.proto

@@ -99,6 +99,15 @@ message Config {
        *    Uses position module configuration to determine TAK PLI broadcast interval.
        */
       TAK_TRACKER = 10;
+
+      /*
+       * Description: Will always rebroadcast packets, but will do so after all other modes.
+       * Technical Details: Used for router nodes that are intended to provide additional coverage
+       *    in areas not already covered by other routers, or to bridge around problematic terrain,
+       *    but should not be given priority over other routers in order to avoid unnecessaraily
+       *    consuming hops.
+       */
+      ROUTER_LATE = 11;
     }
 
     /*

meshtastic/mesh.proto

@@ -1272,6 +1272,13 @@ message MeshPacket {
    * Set by the firmware internally, clients are not supposed to set this.
    */
   uint32 relay_node = 19;
+
+  /*
+   * *Never* sent over the radio links.
+   * Timestamp after which this packet may be sent.
+   * Set by the firmware internally, clients are not supposed to set this.
+   */
+  uint32 tx_after = 20;
 }
 
 /*