[feature] Add ROSEnv generator integration for ROS2 builds

[danimtb]

Changelog: Feature: Add ROSEnv generator integration for ROS2 (Robot Operating System).
Docs: Omit

Related to #17055

This a generator with a new approach: Set the build and run environment before a colcon build in ROS.

The generator should be used together with CMakeDeps and CMaketoolchain generators as it uses the files generated by those as well.

The ROSEnv generator generates a file called 'conanrosenv.bash' that should be sourced before the build.

Example:

$ conan install conanfile.txt --output-folder install/conan
$ source install/conan/conanrosenv.sh
$ colcon build
...
$ source install/setup.bash
$ ros2 run <pkg> <executable>

• Refer to the issue that supports this Pull Request.
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

[memsharded]

Suggested change

	output_folder = self._conanfile.generators_folder
	self.variables.setdefault("CMAKE_TOOLCHAIN_FILE",
	os.path.join(output_folder, "conan_toolchain.cmake"))
	self.variables.setdefault("CMAKE_TOOLCHAIN_FILE",
	os.path.join(self._conanfile.generators_folder, "conan_toolchain.cmake"))

The output_folder is a different concept in Conan, the cli arg --output-folder, better avoid it

[memsharded]

conan install ...
. rosenv => ``conanbuild.sh && . conanrun.sh``
(conanbuid.sh => rosenv.sh)
. conanbuild.sh && . conanrun.sh
colcon build 
. install.setup.bash
execute app