[FEATURE] Add integration with external programs/projects the right way

### Is your feature request related to a problem? Please describe.

Currently there is possible to add external applications on nuttx-apps creating an "external/" directory inside apps/ [1]. However it expects that the added project has the right files inside it (Kconfig, Make.defs, Makefile, CMakelist.txt, etc).

Others RTOSes like zephyr has a similar solution (although they used a confuse name "Module" and that is a bad name since for a kernel a module means dynamic loadable component). Also in their case they expects a directory called "zephyr" inside the target project. Some examples:
https://github.com/open-quantum-safe/liboqs
https://github.com/civetweb/civetweb/tree/master/zephyr
https://github.com/lvgl/lvgl/tree/master/zephyr

This is more than a better solution, this is their way to spread their naming/awareness around all other projects in the Internet and avoids the process of creating a download script in their repository, as we do for LVGL and others.

There is a complete (and verbose) documentation about it here: https://docs.zephyrproject.org/latest/develop/modules.html

1 - It is a hidden feature, there is no Documentation about it: https://nuttx.apache.org/docs/latest/search.html?q=external&check_keywords=yes&area=default

### Describe the solution you'd like

We could follow the same approach, creating a "nuttx" or "NuttX" repository inside other projects simplify the integration process.

### Describe alternatives you've considered

_No response_

### Verification

- [x] I have verified before submitting the report.