Apply fallbackencoding of DicomServices to the DicomDatasets that are sent through this DicomService

[gofal]

Fixes #1642 .

Checklist

• The pull request branch is in sync with latest commit on the fo-dicom/development branch
• I have updated API documentation
• I have included unit tests
• I have updated the change log
• I am listed in the CONTRIBUTORS file

Changes proposed in this pull request:

• If a DicomServer or a DicomClient has a fallbackencoding set, then until now only the reader of incomming data uses this. Now also the writer of outgoing messages applies this fallbackencoding

[amoerie]

One minor consideration related to cloning, but other than that a nice improvement! 👍

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 76.35%. Comparing base (b45ffe1) to head (e91b27b).
Report is 27 commits behind head on development.

Files	Patch %	Lines
FO-DICOM.Core/Network/DicomService.cs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           development    #1780      +/-   ##
===============================================
- Coverage        76.42%   76.35%   -0.07%     
===============================================
  Files              275      275              
  Lines            25410    25417       +7     
  Branches          3043     3046       +3     
===============================================
- Hits             19419    19407      -12     
- Misses            5062     5075      +13     
- Partials           929      935       +6     

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