Feature/509 remove pubsub

[pnoltes]

This PR removes the pubsub feature from Apache Celix.

As stated in #509, pubsub is not part of the OSGi specification, and I believe it would be better for Apache Celix to focus on features from the OSGi spec, perhaps with a few additional small features.

This change should simplify the maintenance of Apache Celix and contribute to its growth as an even more stable framework.

Note that the pubsub feature is still available in the Apache Celix 2.4.x release. Should there be renewed interest in the future, we can consider reintroducing it based on community needs and contributions.

It fixes #466
It fixes #520
It fixes #295
It fixes #222
It fixes #221
It fixes #205
It fixes #123

[codecov-commenter]

Codecov Report

Attention: 27 lines in your changes are missing coverage. Please review.

Comparison is base (2a5058f) 84.25% compared to head (6856982) 88.26%.

❗ Current head 6856982 differs from pull request most recent head efad168. Consider uploading reports for the commit efad168 to get more accurate results

Files	Patch %	Lines
...ration/src/TestExportImportRemoteServiceFactory.cc	83.83%	27 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #703      +/-   ##
==========================================
+ Coverage   84.25%   88.26%   +4.01%     
==========================================
  Files         248      215      -33     
  Lines       31124    24562    -6562     
==========================================
- Hits        26222    21679    -4543     
+ Misses       4902     2883    -2019     

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[PengZheng]

LGTM

I noticed a huge bump in code coverage. If we stick to the new coding convention when refactoring existing code and implementing new functionalities, 95% overall coverage is not a dream.