Add default topic for PublishClient

[TheBurchLog]

Adds a default topic of Namespace.System.Version.Instance for Publish Client

[codecov]

Codecov Report

Attention: 51 lines in your changes are missing coverage. Please review.

Comparison is base (95d48b6) 92.39% compared to head (68b684b) 14.37%.
Report is 11 commits behind head on develop.

❗ Current head 68b684b differs from pull request most recent head 86d3acd. Consider uploading reports for the commit 86d3acd to get more accurate results

Files	Patch %	Lines
brewtils/decorators.py	11.11%	16 Missing ⚠️
brewtils/models.py	20.00%	8 Missing ⚠️
brewtils/rest/publish_client.py	0.00%	6 Missing ⚠️
brewtils/plugin.py	16.66%	5 Missing ⚠️
brewtils/rest/client.py	0.00%	4 Missing ⚠️
brewtils/rest/easy_client.py	0.00%	4 Missing ⚠️
brewtils/rest/system_client.py	0.00%	3 Missing ⚠️
brewtils/schemas.py	0.00%	3 Missing ⚠️
brewtils/__init__.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop     #432       +/-   ##
============================================
- Coverage    92.39%   14.37%   -78.02%     
============================================
  Files           28       28               
  Lines         3644     3686       +42     
============================================
- Hits          3367      530     -2837     
- Misses         277     3156     +2879     

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