Move plugin docs to plugin folders

Summary: Moved plugin documentation and related assets to plugin folders, fixed links and configured redirects where required. Now these docs are used for both showing docs in Flipper and generating Flipper docs website.

Reviewed By: passy

Differential Revision: D29465567

fbshipit-source-id: 3ec4240b215b0d5baea5154f64266a9ba7ead3a5

desktop/plugins/public/leak_canary/docs/setup.mdx

@@ -0,0 +1,43 @@
+Ensure that you already have an explicit dependency in your application's
+`build.gradle` including the plugin dependency, e.g.
+
+```groovy
+dependencies {
+  debugImplementation 'com.facebook.flipper:flipper-leakcanary2-plugin:0.95.0'
+  debugImplementation 'com.squareup.leakcanary:leakcanary-android:2.6'
+}
+```
+
+Update your the `onCreate` method in you `Application` to add the LeakCanary2 plugin to Flipper and the Flipper listener to LeakCanary
+
+```kt
+import com.facebook.flipper.plugins.leakcanary2.FlipperLeakListener
+import com.facebook.flipper.plugins.leakcanary2.LeakCanary2FlipperPlugin
+
+...
+
+  override fun onCreate() {
+    super.onCreate()
+    setupFlipper()
+
+    /*
+    set the flipper listener in leak canary config
+    */
+    LeakCanary.config = LeakCanary.config.copy(
+        onHeapAnalyzedListener = FlipperLeakListener()
+    )
+
+    SoLoader.init(this, false)
+
+    if (BuildConfig.DEBUG && FlipperUtils.shouldEnableFlipper(this)) {
+      val client = AndroidFlipperClient.getInstance(this)
+      /*
+      add leak canary plugin to flipper
+      */
+      client.addPlugin(LeakCanary2FlipperPlugin())
+      client.start()
+    }
+  }
+```
+
+That's it!