add project icon

https://youtrack.jetbrains.com/issue/IJPL-130477/Welcome-screen-only-SVG-can-be-set-as-a-project-icon

https://github.com/openrewrite/rewrite/blob/main/.idea/icon.png

Signed-off-by: Vincent Potucek <vpotucek@me.com>
Signed-off-by: Vincent Potucek <vincent.potucek@sap.com>

Author: pinguin3245678

.gitignore

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