[FEATURE] Github discussions

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

It's fairly hard to find discussions and solutions to problems that others had had with nuttx.

### Describe the solution you'd like

It would be nice to have a casual forum for people using nuttx to interact with. I'm aware that there already is discord server and a mailing list.

Github discussions would allow for more casual developers to get help directly on platform, without relying on third parties like discord and without expecting the formality of the mailing list.

### Describe alternatives you've considered

Discord server
Mailing list

### Verification

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