apps/system/microros: Add .gitignore for library build artifacts.

Ignore build outputs and generated files:
- Directories: micro_ros_src/, micro_ros_dev/, build/, install/
- Build outputs: libmicroros.a, toolchain.cmake, colcon.meta
- Archives: *.tar.gz

Prevents build artifacts and downloaded sources from being committed.

Signed-off-by: Arjav Patel <arjav1528@gmail.com>

system/microros/.gitignore

@@ -0,0 +1,13 @@
+# Build artifacts
+/build/
+/install/
+/micro_ros_dev/
+/micro_ros_src/
+
+# Generated files
+/libmicroros.a
+/toolchain.cmake
+/colcon.meta
+
+# Archives
+*.tar.gz