track mros2 to v0.4.0

[takasehideki]

mros2 v0.4.0 will be released in a few minutes!! But we could not maintain this repository yet. https://github.com/mROS-base/mros2/tree/v0.4.0

This issue is the memo for us to track the latest version of mros2 (but so far,,, ).

• [ ] track mros2 to v0.4.0 (update its submodule)
• [ ] update config/rtps.h
• [ ] consider to track STM32CubeF7
• [ ] remove mros2_user_config.h (also see https://github.com/mROS-base/mros2/commit/8df6a67a3951f248898283efcca02f9a866b7047)
• [ ] add new example echoback_string (also see https://github.com/mROS-base/mros2-mbed/pull/29)
• [ ] test with Humble