bugfix: send html emails in legacy features

[lmoesle]

Description

Short description or comments

Reference

Issues: closes #1109

Check-List

• All Acceptance criteria of user story are met
• JUnit tests are written (60% CodeCov)
• Internal Review is maintained
• Documentations external and internal are completed
• Smoketest successful (Manual E2E-Test depending on Change)
• No Branch waste left
• Board is up-to-date
• Openshift environments are prepared (Secrets, etc.) and release-issue is maintained

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (d68e6dc) 37.67% compared to head (d4c925e) 37.66%.

Files	Patch %	Lines
...gacy/mailing/process/SendMailTemplateDelegate.java	0.00%	1 Missing ⚠️
...ling/process/SendMailTemplateWithLinkDelegate.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                     Coverage Diff                     @@
##             release/2023-december    #1110      +/-   ##
===========================================================
- Coverage                    37.67%   37.66%   -0.01%     
  Complexity                    1258     1258              
===========================================================
  Files                          600      600              
  Lines                         8696     8698       +2     
  Branches                       422      422              
===========================================================
  Hits                          3276     3276              
- Misses                        5287     5289       +2     
  Partials                       133      133              

Flag	Coverage Δ
unittests	37.66% <33.33%> (-0.01%)	⬇️

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[simonhir]

@lmoesle glaub das in dem Bug war per Element-Template direkt auf die Integration, würde das dann nicht noch fehlen?
Und hatte es gestern auch einmal probiert, da wurden Umlaute in der Mail bzw. im speziellen beim Button mit "Task öffnen" nicht korrekt angezeigt. Das müsste ja dann auch ein anderes Problem sein oder?