feat: Add mqtt_gateway application and .gitignore

Signed-off-by: Eduard Iten <eduard@iten.pro>

.gitignore

@@ -1 +1,65 @@
 **/build
+
+# Zephyr build directories
+build/
+build-*/
+*/build/
+**/build/
+
+# Zephyr out-of-tree build directories
+out-of-tree-build/
+
+# Files generated by the build system
+zephyr.elf
+zephyr.bin
+zephyr.hex
+zephyr.map
+zephyr.strip
+zephyr.lst
+zephyr.asm
+zephyr.stat
+zephyr.a
+zephyr.o
+*.o
+*.a
+*.so
+*.so.*
+*.dll
+*.exe
+
+# Cmake
+CMakeCache.txt
+CMakeFiles/
+cmake_install.cmake
+CTestTestfile.cmake
+compile_commands.json
+
+# Kconfig generated files
+.config
+.config.old
+autoconf.h
+
+# Doxygen
+doxygen/
+
+# west
+.west/
+west.yml.bak
+
+# Editor-specific files
+.vscode/
+.idea/
+*.swp
+*~
+*.bak
+*.orig
+
+# Python
+__pycache__/
+*.pyc
+
+# Mac OS X
+.DS_Store
+
+# Windows
+Thumbs.db