Configure required IDEA plugins (#84674)

Closes #53812.

The CheckStyle-IDEA and EcliseCodeFormatter IDEA plugins are to all
intents and purposes required when using IntelliJ to work on
Elasticsearch, so add configuration that marks then as required.

.gitignore

@@ -9,10 +9,12 @@ build-idea/
 out/
 
 # include shared intellij config
-!.idea/scopes/x_pack.xml
+!.idea/checkstyle-idea.xml
+!.idea/eclipseCodeFormatter.xml
+!.idea/externalDependencies.xml
 !.idea/inspectionProfiles/Project_Default.xml
 !.idea/runConfigurations/Debug_Elasticsearch.xml
-!.idea/checkstyle-idea.xml
+!.idea/scopes/x_pack.xml
 
 # These files are generated in the main tree by IntelliJ
 benchmarks/src/main/generated/*

.idea/externalDependencies.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalDependencies">
+    <plugin id="EclipseCodeFormatter" />
+    <plugin id="CheckStyle-IDEA" />
+  </component>
+</project>