[Angular] Add tests for MetricsModalThreadsComponent

[qmonmert]

Add tests and improve coverage: https://sonarcloud.io/component_measures?id=jhipster-sample-application&metric=coverage&selected=jhipster-sample-application%3Asrc%2Fmain%2Fwebapp%2Fapp%2Fadmin%2Fmetrics%2Fblocks%2Fmetrics-modal-threads%2Fmetrics-modal-threads.component.ts

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Please make sure the below checklist is followed for Pull Requests.

• All continuous integration tests are green
• Tests are added where necessary
• The JDL part is updated if necessary
• jhipster-online is updated if necessary
• Documentation is added/updated where necessary
• Coding Rules & Commit Guidelines as per our CONTRIBUTING.md document are followed

When you are still working on the PR, consider converting it to Draft (below reviewers) and adding skip-ci label, you can still see CI build result at your branch.

[qmonmert]

https://sonarcloud.io/component_measures?id=jhipster-sample-application&metric=coverage&selected=jhipster-sample-application%3Asrc%2Fmain%2Fwebapp%2Fapp%2Fadmin%2Fmetrics%2Fblocks%2Fmetrics-modal-threads%2Fmetrics-modal-threads.component.ts

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After