Introduce interface for topic event subscriber

[mfcollins3]

Description

I introduced the TopicEventSubscriber interface and added an AddTopicEventSubscriber method to the Server interface. TopicEventSubscriber will allow more complex subscribers to be registered that are using structs so that dependencies like sql.DB objects or other parameters can be provided to subscribers and used to process incoming events.

I modified TopicRegistrar to register and store TopicEventSubscriber instead of TopicEventHandler in the TopicRegistration struct. I created an adapter for TopicEventHandlerso that it implements the newTopicEventSubscriber` interface and can continue to be used without modification.

• I introduced the TopicEventSubscriber type instead of rewriting the TopicEventHandler type to not break existing code. I used the pattern that net/http uses for Handler and HandlerFunc.
• I did not define any new tests, but I modified the existing tests to work. Given the way that I changed TopicRegistration and making TopicEventHandler implement TopicEventSubscriber, I didn't think that any additional tests were necessary.

Issue reference

Please reference the issue this PR will close: #660

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 61.56%. Comparing base (6c59092) to head (2528b25).
Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
service/http/topic.go	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #661      +/-   ##
==========================================
- Coverage   62.52%   61.56%   -0.96%     
==========================================
  Files          56       58       +2     
  Lines        4139     4296     +157     
==========================================
+ Hits         2588     2645      +57     
- Misses       1425     1521      +96     
- Partials      126      130       +4     

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[mikeee]

lgtm

[yaron2]

Thanks for your contribution!