draft: RFC5424 origin structure added

[vasiliyk]

draft: RFC5424 origin structure added; addressing #225

What I don't like:

1. default stumpless_element_to_string function returns the origin structure in an incorrect format. Correct format should be: [origin ip="example.ip" software="stumpless" swVersion="example.version"]. Should I override function to account for it?
2. stumpless syslog and vsyslog replacements don't return origin structure by default. Should an option be added to them to include origin structure?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 54 lines in your changes missing coverage. Please review.

Project coverage is 89.13%. Comparing base (f3ac58e) to head (ac9cef1).

Files with missing lines	Patch %	Lines
src/log.c	0.00%	54 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           latest     #479      +/-   ##
==========================================
- Coverage   90.22%   89.13%   -1.10%     
==========================================
  Files          47       47              
  Lines        4410     4464      +54     
  Branches      592      604      +12     
==========================================
  Hits         3979     3979              
- Misses        288      342      +54     
  Partials      143      143              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[goatshriek]

This will be quite a difficult addition, since there isn't an example/base set up for automatic elements yet.

The code to gather the IP addresses will need to be put into configuration source files and chosen based on the headers available, rather than the availability of WIN32. You can look at include/private/config/wrapper/network_supported.h to see the logic for this now. It would probably make the most sense to add to this, although the use of ifaddrs.h may warrant it's on header check and inclusion.

The automatic elements should be configurable, on by default, and not do too much special work apart from just creating and adding the element to entries before they're logged. For now, maybe adding a boolean flag to the target structure on whether or not automatic elements are enabled and then doing the extra work to add the element in stumpless_add_entry, or even better in format_entry is the best first step. This will allow you to bypass the concerns you note about the to_string format being incorrect, and the other syslog and vsyslog functions will still pick up these changes as well.

Also, be sure that you have some sort of test so that elements with the automatic element can be verified to have the correct data.