initial implementation of the event broker

[walshmm]

Short description of the changes:

This pr implements the event broker as specified by ewm 13858

Check list for the pull request

• I have read the [CONTRIBUTING]
• I have read the [CODE_OF_CONDUCT]
• I have added tests for my changes
• I have updated the documentation accordingly

Check list for the reviewer

• I have read the [CONTRIBUTING]
• I have verified the proposed changes
• best software practices
  • all internal functions have an underbar, as is python standard
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

Manual test for the reviewer

References

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.48%. Comparing base (502f0ab) to head (72298ca).
⚠️ Report is 1 commits behind head on next.

Additional details and impacted files

@@            Coverage Diff             @@
##             next      #58      +/-   ##
==========================================
+ Coverage   82.51%   88.48%   +5.97%     
==========================================
  Files           6        9       +3     
  Lines         223      304      +81     
==========================================
+ Hits          184      269      +85     
+ Misses         39       35       -4     

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