Updates Yarn version and packages used (#436)

.gitignore

@@ -25,6 +25,3 @@ node_modules/
 ### IDE
 *.iml
 *.idea
-
-### Other
-war/.yarnrc.yml

docs/CONTRIBUTING.adoc

@@ -12,13 +12,16 @@ When building, Yarn will bundle the front-end files only.
 . Install tools
 .. Java 17
 .. Maven 3.8.6
-.. Node 18.10.0 and Yarn 3.2.4 (these should be done in the "war" directory)
+.. Node 20.10.0 and Yarn 4.0.2 (these should be done in the "war" directory)
 .. Optional: have Docker installed in your environment
 . Open the project in your favorite IDE.
 
 NOTE: Optionally, you can use the Maven wrapper in the repository.
 In that case, replace the `mvn` command by `./mvnw` in the command listed bellow.
 
+WARNING: Make sure that you follow the instruction to install Yarn 2+.
+See https://yarnpkg.com/getting-started/install.
+
 Please see the link:ARCHITECTURE.adoc[architecture] document to better understand the structure of the code.
 
 == How to build locally the application

war/.yarnrc.yml

@@ -0,0 +1,4 @@
+compressionLevel: mixed
+enableGlobalCache: false
+nodeLinker: node-modules
+yarnPath: .yarn/releases/yarn-4.0.2.cjs

war/package.json

@@ -1,6 +1,6 @@
 {
   "name": "plugin-health-scoring",
-  "packageManager": "yarn@3.2.4",
+  "packageManager": "yarn@4.0.2",
   "license": "MIT",
   "private": true,
   "scripts": {