ims_registrar_pcscf: Add support for sec-agree parameters parsing

[tdimitrov]

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 nutshell, this PR adds support for sec-agree parameters parsing in PCSCF.

ims_usrloc_pcscf can store security related parameters from sec-agree extension. However ims_register_pcscf doesn't parse the corresponding SIP headers. This PR adds code, which parses security-client header fields and stores them via ims_usrloc_pcscf.

[miconda]

Thanks for contribution! Hopefully @ngvoice or @jaybeepee have time to check a bit before merging.

[ngvoice]

Thanks! Looks okay!