Fix custom webhook request body format

[zhongnansu]

Description

• remove the forced "Content" key for custom webhooks, as the custom webhook server can require any format. User may provide json which contains customized format.
• remove title for custom webook message, since newline breaks JSON format input.
• Fix the issue that some unit test using junit4 not being picked up, by replacing with jupiter
• change common-utils branch name in CI to main
• suppport http as url protocol in webhook

Issues Resolved

#245
#232

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[zhongnansu]

CI is failing, but it passed locally. I also try re-run CI on HEAD of dev branch. It fails too
@dai-chen could you help take a look at the issue?

[codecov-commenter]

Codecov Report

Merging #248 (a612ae1) into develop (5cad6a6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #248   +/-   ##
========================================
  Coverage    80.53%   80.53%           
========================================
  Files           60       60           
  Lines         1634     1634           
  Branches       415      415           
========================================
  Hits          1316     1316           
  Misses         310      310           
  Partials         8        8           

Flag	Coverage Δ
dashboards-notifications	80.53% <ø> (ø)

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[davidcui1225]

How come we changed the Test import?

[zhongnansu]

we are using junit5, but this one is still junit4, it doesn't throw error, but actually the tests are not picked up. We should use junit 5 anywhere

[davidcui1225]

just one question