scheduler: change reservation event message format

[zwzhang0107]

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 68.60%. Comparing base (b49c575) to head (ad71ae9).
Report is 3 commits behind head on main.

Files	Patch %	Lines
.../frameworkext/eventhandlers/reservation_handler.go	83.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2090      +/-   ##
==========================================
- Coverage   68.61%   68.60%   -0.02%     
==========================================
  Files         430      430              
  Lines       39665    39654      -11     
==========================================
- Hits        27217    27203      -14     
- Misses      10096    10097       +1     
- Partials     2352     2354       +2     

Flag	Coverage Δ
unittests	68.60% <83.33%> (-0.02%)	⬇️

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[saintube]

/lgtm

[ZiMengSheng]

/approve

[koordinator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ZiMengSheng

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