Refactor/rt pub define

[firesurfer]

This is a followup PR for #210

The approach in general probably needs some discussion. But I think it is a first step into removing conditional compilation based on a define set in a different file.

This implementation keeps the ability to select the polling mode via the define but prints a deprecation message.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.63014% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.00%. Comparing base (1ce4df7) to head (94e0298).

Files with missing lines	Patch %	Lines
include/realtime_tools/realtime_publisher.hpp	98.63%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
+ Coverage   72.72%   75.00%   +2.27%     
==========================================
  Files           7        7              
  Lines         429      468      +39     
  Branches       71       78       +7     
==========================================
+ Hits          312      351      +39     
  Misses         73       73              
  Partials       44       44              

Flag	Coverage Δ
unittests	75.00% <98.63%> (+2.27%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
include/realtime_tools/realtime_publisher.hpp	97.70% <98.63%> (+1.86%)	⬆️