gitignore: Add missing entries from af3 repo

Issue-Ref: 3620
Issue-Url: https://af3-developer.fortiss.org/issues/3620


Signed-off-by: Alexander Diewald <diewald@fortiss.org>

.gitignore

-/*/bin/
-/*/build/
-/*/generated-src/
+/*/bin/
+/*/build/
+/*/generated-src/
+/*/target/
+*.rej
+.DS_Store
+._.DS_Store