Fix the authorization header for re-REGISTER, REF 14600

The commit contains 2 fixes making the authorization header is cached during initial registration
and then reused for further re-REGISTER requests.
- Enable flags in pjproject so the authorization header is cached and then automatically included
  in next re-REGISTER requests.
- Set initial registration outbound authentication credentials properly so the following error in
  pjproject is fixed and authorization header is cached properly:
  pjproject: <?>: sip_auth_clien ...Unable to set auth for tdta0x: can not find credential for
  X.X.X.X/Digest