Add a project icon for IntelliJ IDEA

The icon comes from https://spring.io/img/projects/spring-framework.svg.

Closes spring-projectsgh-34444
Signed-off-by: Vincent Potucek <[email protected]>

Author: pinguin3245678

.gitignore

@@ -42,7 +42,8 @@ spring-*/src/main/java/META-INF/MANIFEST.MF
 *.iml
 *.ipr
 *.iws
-.idea
+.idea/*
+!.idea/icon.svg
 out
 test-output
 atlassian-ide-plugin.xml