[NXDART] GitHub Pull Request integration.

### Task Goals

* Find a way to attach DRUNX to `apache/nuttx` [1] and `apache/nuttx-apps` [2] repositories in order to intercept incoming changes and verify build/runtime them yet before these are merged into master causing problems.
* GitHub REST API for Pull Requests reference [3] https://docs.github.com/en/rest/pulls?apiVersion=2022-11-28.
* GitHub REST API for Issues reference [4]: https://docs.github.com/en/rest/issues/issues?apiVersion=2022-11-28.

[1] https://github.com/apache/nuttx
[2] https://github.com/apache/nuttx-apps
[3] https://docs.github.com/en/rest/pulls?apiVersion=2022-11-28
[4] https://docs.github.com/en/rest/issues/issues?apiVersion=2022-11-28

### Possible Solutions

* Yes it PR build and runtime tests are possible using GitHub PR REST API and @lupyuen already did a working prototype.
* There are many and serious security concerns regarding running untrusted code and scripts, therefore it needs additional security mechanisms implementation (i.e. jails, containers, virtualization), as well as fetch->build->run stages separation so scripts will have no internet connectivity (like FreeBSD Ports), but that impacts existing configurations that needs an update (lots of work).
* Therefore for now only manually pre-reviewed code can be verified by manual trigger of testbot actions.
* Full autonomous functionality when security mechanisms and build updates are in place.