Implement distributed scheduler building block

[mikeee]

Description

• Registers a new alpha appcallback server
• Implements an empty onbulktopicevent handler that will panic
• Implements the alpha job api and appcallback registration
• Misc changes to the examples - fixing conflicts with the default scheduler port
• Updates the validation workflow to enable building from custom commits using events

Issue reference

Please reference the issue this PR will close: #561

Checklist

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

• [x] Code compiles correctly
• [x] Created/updated tests
• [ ] Extended the documentation

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 49.31507% with 37 lines in your changes missing coverage. Please review.

Project coverage is 61.72%. Comparing base (27248ba) to head (30601f2). Report is 20 commits behind head on main.

Files	Patch %	Lines
service/grpc/scheduling.go	0.00%	21 Missing :warning:
client/scheduling.go	78.37%	4 Missing and 4 partials :warning:
service/http/scheduling.go	0.00%	6 Missing :warning:
service/grpc/topic.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #562 +/- ## ========================================== + Coverage 58.04% 61.72% +3.68% ========================================== Files 55 56 +1 Lines 3568 3420 -148 ========================================== + Hits 2071 2111 +40 + Misses 1375 1184 -191 - Partials 122 125 +3 ```

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[yaron2]

What's needed for this to go out of draft?

[mikeee]

What's needed for this to go out of draft?

I've rerun this and the jobs aren't being invoked (not sure what has changed since the last successful runs a month ago). I'll need to take a look at this tomorrow with fresh eyes

[mikeee]

The answer was right there in the error as always... needed to register a new alpha callbackserver since this was refactored upstream.

[yaron2]

@mikeee this looks great from my side. ready to merge?