Add repository dispatch event

[mxandeco]

Description

The changes here will expose the "create dispatch event" on the repository object, as describe on the github api:

https://docs.github.com/en/rest/reference/repos#create-a-repository-dispatch-event

The main usage of the api is to trigger an action or webhook from outside github, github has no apis to retrieve dispatches from a repo, and the ack we get from the api in case of success is a 204 status response.

Covers the issue #1246

[codecov]

Codecov Report

Merging #1248 (aefe8d3) into main (b92c060) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1248      +/-   ##
============================================
+ Coverage     77.42%   77.45%   +0.02%     
- Complexity     1899     1900       +1     
============================================
  Files           189      189              
  Lines          5972     5979       +7     
  Branches        327      327              
============================================
+ Hits           4624     4631       +7     
  Misses         1150     1150              
  Partials        198      198              

Impacted Files	Coverage Δ
src/main/java/org/kohsuke/github/GHRepository.java	68.42% <100.00%> (+0.34%)	⬆️

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