posix: implement putmsg()

[ycsin]

This is part of the See POSIX Roadmap for LTSv3 (RFC #51211).

putmsg() is required as part of _XOPEN_STREAMS Option Group.

For more information, please refer to https://pubs.opengroup.org/onlinepubs/9699919799/functions/putmsg.html

[uddivert]

Hey, I would like to tackle this issue.

I am new to zephyr is there any information about how to get started, and possible approaches this, and testing my implementation?

[ycsin]

Hey, I would like to tackle this issue.

I am new to zephyr is there any information about how to get started, and possible approaches this, and testing my implementation?

This reply is probably a little too late, some pointers for you in case you haven't read them already:

• Zephyr Getting Started Guide
• Tests are written in the ztest framework, you can read more about it here
• We run tests with Twister in Zephyr, you can read more about it here

You may also take a look at #67711, which closed this issue, since @AbhinavMir is also a first-time contributor, there might be some answers in the PR.