pkg: add example script to create tarball with submodules instantiated

[space88man]

In preparation for packaging of tls_wolfssl, add an example script to create source tarball with submodule code.

• add mock configs and instructions for packaging locally
• add convenience script to create a src.rpm

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

In preparation for packaging tls_wolfssl the distributed source tarballs need to have the submodule instantiated and archived with the primary source code. This is an example script to package submodule code with the primary code.

It can be used in CI/CD to prepare the tarball.

Subsequently I will update the pkg/ scripts to enable packaging of tls_wolfssl.

Pinging @sergey-safarov.

[miconda]

If reusing misc/scripts/ location does not seem a good option, I think it is better at least to have the folder relocated to pkg/kamailio/scripts/ instead of pkg/scripts/.

[space88man]

If reusing misc/scripts/ location does not seem a good option, I think it is better at least to have the folder relocated to pkg/kamailio/scripts/ instead of pkg/scripts/.

Done and pushed.

Update: rebased to @ f04f853

[miconda]

Thanks!