Add locks to starboard and include example of level-only starring (#125)

backend/src/plugins/Starboard/StarboardPlugin.ts

@@ -88,6 +88,25 @@ export const StarboardPlugin = zeppelinGuildPlugin<StarboardPluginType>()("starb
                 basic:
                   enabled: true
       ~~~
+
+      ### Limit starboard to a specific level (and above)
+      This is identical to the basic starboard above, but only works for a specific level (>=50).
+      
+      ~~~yml
+      starboard:
+        config:
+          boards:
+            levelonly:
+              enabled: false # The starboard starts disabled and is then enabled in a level override below
+              channel_id: "604342689038729226"
+              stars_required: 1
+        overrides:
+          - level: ">=50"
+            config:
+              boards:
+                levelonly:
+                  enabled: true
+      ~~~
     `),
   },
 

backend/src/plugins/Starboard/events/StarboardReactionAddEvt.ts

@@ -58,6 +58,7 @@ export const StarboardReactionAddEvt = starboardEvt({
       });
 
     for (const starboard of applicableStarboards) {
+      const boardLock = await pluginData.locks.acquire(`starboards-channel-${starboard.channel_id}`);
       // Save reaction into the database
       await pluginData.state.starboardReactions.createStarboardReaction(msg.id, userId).catch(noop);
 
@@ -73,6 +74,7 @@ export const StarboardReactionAddEvt = starboardEvt({
       if (reactionsCount >= starboard.stars_required) {
         await saveMessageToStarboard(pluginData, msg, starboard);
       }
+      boardLock.unlock();
     }
   },
 });